Learning Objectives Heat Transfer Equipment Overview Core Types of Heat Exchangers and Their Common Applications in Oil and Gas Processing Facilities By the end of this lesson, you will be able to: By the end of this lesson, you will be able to: Identify types of heat exchangers and common applications in oil and gas processing facilities 1 1
Heat Exchanger Types and Applications Heat Exchanger Types and Applications 2 2
Heat Exchanger Types and Applications Heat Exchanger Types and Applications 3 3
Heat Exchanger Types and Applications Heat Exchanger Types and Applications 4 4
Heat Exchanger Types and Applications Heat Exchanger Types and Applications 5 5
Heat Exchanger Types and Applications Heat Exchanger Types and Applications 6 6
Heat Exchanger Types and Applications Heat Exchanger Types and Applications 7 7
Heat Exchanger Types and Applications Types of Heat Transfer Equipment Fluid-Fluid Shell-and-tube Compact Pipe-in-pipe Plate exchangers Brazed aluminum (plate-fin) Printed circuit Spiral Coil Special types for specific services Fired Heaters (Radiant Heat Transfer) Direct Indirect Coolers Utilizing Air Air-cooled heat exchangers (ACHE) Cooling towers Combination air-water 8 8
Shell and Tube Heat Exchangers Most common and most versatile exchanger type Can handle a wide range of fluids single phase and multiphase Robust construction Variety of fabrication materials possible Heavy Relatively large footprint Expensive Compact Heat Exchangers Applications in the oil and gas industry have grown significantly over the past 20-30 years Relative to shell and tube exchangers: Smaller size and weight Decreased temperature approach and higher efficiency Lower cost, especially when expensive materials of construction are required Several types of compact exchangers: Plate Core-and-Kettle Brazed Aluminum Plate-Fin (BAHX) Pipe-In-Pipe Printed Circuit (PCHE) Pipe Coils 9 9
Fired Heaters Fired heaters are the most common type for high temperatures Direct Fired Heaters Two types: Combustion in a fire box, process fluid flows through the tubes (used for larger duties) Combustion in a fire tube usually immersed in the process fluid (used for smaller duties) Indirect Fired Heaters Typically a fire tube heater, fire tube immersed in heat transfer fluid Water used as heat transfer fluid in lower temperature applications Molten eutectic salts used in higher temperature applications Heat transfer to the process fluid occurs in a second tube bundle, which is immersed in the heat transfer fluid Coolers Utilizing Air Air-Cooled Heat Exchangers (ACHE) Most popular in onshore facilities Not as popular offshore due to large footprint Low environmental impact Cooling Towers Air supplies cooling by evaporating water Water is the heat transfer fluid More efficient than air coolers, but Higher CAPEX and environmental impact Not widely used in upstream and midstream applications More popular in refineries and chemical plants Combination Air-Water 10 10
Learning Objectives You are now able to: Identify types of heat exchangers and common applications in oil and gas processing facilities Heat Transfer Equipment Overview Core Heat Transfer Mechanisms and Parameters Affecting Heat Transfer Coefficient 11 11
Learning Objectives By the end of this lesson, you will be able to: By the end of this lesson, you will be able to: Describe heat transfer mechanisms: conduction, convection and radiation Define heat transfer coefficient and describe the primary parameters that affect its value Heat Transfer Mechanisms Heat is energy transferred as a result of a temperature difference Conduction Transfer of thermal energy through a substance due to a temperature gradient Convection Transfer of thermal energy due to bulk fluid motion caused by the presence of a temperature gradient and its effect on fluid properties Relative magnitude (1-Lowest and 4-Highest): 1. Conduction 2. Natural Convection 3. Laminar Forced Convection 4. Turbulent Forced Convection Radiation A hot body radiates heat that may be absorbed, reflected or transmitted to a colder body 12 12
Tube Wall Conduction Heat Transfer Combined Convection & Conduction Heat Transfer Q Q T1 T4 1 ln(r o / ri ) 1 ha 2 k L h A convection Q (k)(driving Force) Resistance Force (k W )(L t ) ln( r / r) / (2 ) o i i W o i conduction o convection Q = heat transferred W Btu/hr SI FPS h o, h i = inside & outside fluid film coefficient W/m 2 - C Btu/hr-ft 2 - F A o, A I, = area for heat transfer m 2 ft 2 r o, r I, = tube outside and inside radius m ft L = tube length m ft k w = thermal conductivity of solid wall W/m- C Btu/hr-ft- F T 1 T 4 = temperature difference C F T T 1 2 13 13
Overall Heat Transfer Coefficient, U o 1 ln 1 2 1 1 Do D o ln(d o / D i ) 1 U hd 2k L h Tube (A o = πd o L and A i = πd i L) U o = overall heat transfer coefficient based on the outside tube wall area h o = film coefficient on the outside of the tube h i = film coefficient on the inside of the tube Fouled Overall Heat Transfer Coefficient, U o Tube (A o = πd o L and A i = πd i L) Do Doln(D o / D i) Do f i f o o i i 2 W o i 1 1 U hd k L h D U o = overall heat transfer coefficient based on the outside tube wall area h o = film coefficient on the outside of the tube h i = film coefficient on the inside of the tube k w = thermal conductivity of tube wall o i i W o k w = thermal conductivity of tube wall D o = outside tube diameter D i = inside tube diameter D o = outside tube diameter D i = inside tube diameter f i = fouling factor on the inside of the wall f o = fouling factor on the outside of the wall 14 14
Temperature Gradient Through a Fouled Pipe Wall Fouling Factors Avoid using fouling factors as an arbitrary safety factor Empirical and estimated from actual operating data Fouling is dependent upon the velocity of the fluid in the exchanger Rule of Thumb: The fouling factors should not contribute more than 20% excess area to the HEX design If fouling factors have been specified, vendors typically provide heat exchanger data sheets with U clean and U service performance Clean overall heat transfer coefficient U clean will be greater than service overall heat transfer coefficient U service 15 15
Overall Heat Transfer Coefficients Effect of Velocity on Performance Correlations like these are not recommended for design calculations, but are useful for planning or scoping studies Calculation of overall heat transfer coefficient U o from the equation on the previous slides may be necessary Values of thermal conductivity, k, and film heat transfer coefficient, h, are required Fluid velocity has a significant effect on exchanger performance For flow inside a tube: For flow outside a tube: h i v 0.8 As velocity increases, h increases and therefore U o increases; for a given heat exchanger area, the heat exchanger duty increases as velocity increases Typical Tube Side Velocities h o v 0.6 16 16
Effect of Velocity on Pressure Drop As the fluid velocity increases, the pressure drop also increases For flow inside a tube: P v 1.8 Example Design Pressure Drops (Application specific but these are typical values) Learning Objectives You are now able to: Describe heat transfer mechanisms: conduction, convection and radiation. Define heat transfer coefficient and describe the primary parameters that affect its value. 17 17
Learning Objectives Heat Transfer Equipment Overview Core Estimating Exchangers Heat Transfer Area By the end of this lesson, you will be able to: By the end of this lesson, you will be able to: Describe the rate equation used to calculate heat transfer area Describe the effective temperature difference and explain how it affects heat transfer area Estimate heat transfer surface area required for a heat exchanger application 18 18
Rate Equation Temperature Temperature (a) Hot End T 2 Temperature T eff Hot End T 2 Heat Transferred, Q Heat Transfer Equation Cold End T 1 Where: Q = heat transfer rate U o = overall heat transfer coefficient A = (a) Heat exchanger area t eff = Effective temperature difference Rate Equation (a) Hot End T 2 T eff Heat Transferred, Q Heat Transfer Equation Cold End T 1 Where: Q = heat transfer rate U o = overall heat transfer coefficient A = Heat exchanger area t eff = Effective temperature difference T eff is the effective temperature difference in the exchanger For conventional exchanger configurations and no phase change, it can be estimated from a simple average equation Cold For more complex exchangers End and a phase change in one or both of the fluids, it can be estimated by dividing the exchanger into sections and using T numerical integration 1 The smaller the effective temperature difference, the more surface area required Heat Transferred, Q T eff is the effective temperature difference in the exchanger For conventional exchanger configurations and no phase change, it can be estimated from a simple average equation For more complex exchangers and a phase change in one or both of the fluids, it can be estimated by dividing the exchanger into sections and using numerical integration The smaller the effective temperature difference, the more surface area required 19 19
Effective Temperature Difference Schematics Effective Temperature Difference Schematics Example: oil being cooled with water 20 20
Effective Temperature Difference Schematics Example: oil being cooled with water Effective Temperature Difference Schematics 21 21
Effective Temperature Difference Schematics Example: chiller in a gas processing facility Effective Temperature Difference Schematics Example: gas-gas exchanger 22 22
Effective Temperature Difference Schematics Example: gas being cooled by a multicomponent refrigerant, or side reboiler on a de-methanizer using feed gas as the heat source Log Mean Temperature Difference Assumptions: 1. The heating and cooling curves are linear 2. The physical properties of the fluids do not significantly change in the exchanger ln Where: T lm = Log mean temperature difference, LMTD T eff = Temperature difference corrected for heat exchanger configuration F = TEMA MTD Correction Factor t 1 = Largest T (at one end of the heat exchanger) t 2 = Smallest T (at one end of the heat exchanger) 23 23
Suggested Approach Temperatures The minimum temperature approach is an economic choice As T 2 decreases, T eff decreases and the required heat transfer area increases. This increase can be significant as T eff approaches zero. Smaller values of T 2 decrease utility costs (power and fuel) because there is less lost work in the heat transfer process. The minimum approach may occur at the hot end or the cold end of the exchanger depending on the application. The minimum approach may also occur inside the exchanger. Suggested Approach Temperatures The minimum temperature approach is an economic choice 24 24
Energy Balance T 3 3 m 34 T 2 2 *C p can be used when no phase change occurs. 1 m 12 Learning Objectives T 1 4 T 4 In a fluid exchanger, the energy balance for each fluid reduces to H = Q The Q of one fluid = the Q of the other fluid if one ignores heat losses to, or heat gains from, surroundings Heat loss or gain is normally considered to be zero in exchanger heat balances You are now able to: Describe the rate equation used to calculate heat transfer area Describe the effective temperature difference and explain how it affects heat transfer area Estimate heat transfer surface area required for a heat exchanger application 25 25
Learning Objectives Heat Transfer Equipment Overview Core Shell and Tube Exchanger Types and Their Applications By the end of this lesson, you will be able to: By the end of this lesson, you will be able to: Describe shell and tube exchanger types and applications 26 26
Shell and Tube Exchangers TEMA: Tubular Exchanger Manufacturers Association TEMA defines three classes of mechanical standards: Class R Class B Class C Designation of exchanger shown below: AKT (Courtesy Tubular Exchanger Mfgrs. Assn. ) Fixed Tubesheet, Straight Tube Advantages: Lowest cost of any TEMA type, especially type NEN Provides the maximum surface area for a given shell and tube diameter Can be constructed with multiple tube passes to optimize tube velocity Disadvantages: Shell side can only be cleaned by chemical methods Differential thermal expansion Most common application of this exchanger type: gas-gas exchanger Expansion joint Type BEM 27 27
Fixed Tubesheet, Straight Tube This TEMA type is the simplest design (others include BEM, AEM, NEN) The tubesheet is welded to the shell The heads are either bolted to the tubesheet or, in the NEN design, welded to the tubesheet Type BEM Expansion joint Removable Bundle, Floating Head w/internal Split Ring This TEMA Type is widely used for applications requiring frequent tube bundle removal for inspection and cleaning Advantages: Floating head design allows for differential thermal expansion between the shell and tube bundle Inside of shell can be inspected and cleaned Tubes can be mechanically cleaned (square layout only) Less expensive per unit of surface area than pull-through designs Split backing ring Type AES 28 28
Removable Bundle, Floating Head w/internal Split Ring Disadvantages: Higher maintenance than pull-through designs: shell cover, split backing ring and floating head cover must be removed to pull tube bundle More expensive than fixed tubesheet or U-tube types Applications: Those requiring frequent tube bundle removal for inspection and cleaning For large differential temperatures between the shell and tube fluids Removable U-Tube Bundle Split backing ring Type AES This TEMA Type is widely used for applications requiring frequent tube bundle removal for inspection and cleaning Advantages: Allows for differential thermal expansion between the shell and the tube bundle as well as for individual tubes Inside of shell can be inspected and cleaned Less costly than floating head designs Removable tube bundle Capable of withstanding thermal shock applications. Type CFU 29 29
Removable U-Tube Bundle Disadvantages: U-tubes cannot be mechanically cleaned Individual tubes are difficult to replace Single tube passes or true countercurrent flow is not possible Tube wall thickness in the U-bend is thinner than in straight portion of tubes Applications: Oil, chemical and water heating applications Other Designs Type CFU Pull through floating heads (TEMA Type T) Easier maintenance than S type because there is no backing ring Lower surface area per shell diameter than S and U types Outside packed floating head (Type P) and externally sealed floating tubesheet (Type W) Not suitable for most oil and gas applications because of limited integrity of sealing mechanism and the flammability and toxicity of fluids Shell (Types G, H, J and X) Type G and H shells are often used in low pressure drop applications, such as thermosiphon reboilers J-type (divided flow) shells shorten the shellside fluid flow path; these are often used in low pressure-drop applications X-type (crossflow) shells are also used in very low pressure-drop services such as condensers; multiple inlet and outlet nozzles can be used 30 30
Tubes 60 Triangular 30 Rotated Triangular Baffles 90 Square 45 Rotated Square Baffles support the tube bundle and increase the heat transfer coefficient by forcing the shell-side fluid to traverse the tube bundle several times The baffle cut is expressed as a fraction of inside shell diameter; typical baffle cuts range from 0.2 to 0.35 The opening is often called the baffle window, and should provide roughly the same flow area as the crossflow area between the baffles The distance between the baffles is termed the baffle pitch; it typically ranges from 20-50% of the shell diameter More baffles result in higher shell side heat transfer coefficient and pressure drop The most common type is the single segmental baffle The most common tube diameter is 19 mm [3/4 in] Triangular is the most common layout Larger tubes are easier to clean and are sometimes used in severe fouling services A square layout is preferred in removable tube bundle applications, because it is easier to clean Both triangular and square layouts can be rotated to achieve more desirable performance Baffle window Baffle cut 31 31
Fluid Placement Shell-Side 1. Viscous fluid 2. Fluid having the lower flowrate 3. Boiling fluid 4. Condensing fluids in total condensers 5. Fluid having lower available pressure drop Learning Objectives Tube-Side 1. Toxic and lethal fluid 2. Corrosive fluid 3. Fouling fluid 4. High temperature fluid 5. High pressure fluid 6. Fluid requiring inhibitor injection 7. Partially condensing fluid You are now able to: Describe shell and tube exchanger types and applications 32 32
Learning Objectives Heat Transfer Equipment Overview Core Compact Heat Exchangers and Fired Heaters By the end of this lesson, you will be able to: By the end of this lesson, you will be able to: Describe compact heat exchangers and fired heaters 33 33
Gasketed Plate Heat Exchangers (PHE) Common applications include sea water-cooling medium exchange and crude oil coolers offshore Onshore, they have been used in low pressure fluid-fluid applications, such as lean-rich amine and lean-rich glycol exchangers Gasketed PHEs Advantages and Disadvantages (Courtesy of Tranter) 34 34
Example: Shell & Tube vs. Plate Heat Exchanger Schematic of a Semi-Welded PHE (Courtesy ITT Industries) Used for refrigeration applications (condensing and boiling) on the welded side of the exchanger 35 35
Block Style Fully Welded PHE Panel Upper head Heat transfer plate pack Gasket Baffle Support Girder Lower head (Courtesy Alfa Laval) Used for TEG dehydration (lean/rich exchanger) amine sweetening, and fractionation tower condenser The block style fully welded PHE is used frequently, where leaks could be hazardous to personnel or the environment Welded PHEs Advantages and Disadvantages The advantages and disadvantages of welded plate exchangers are similar to the gasketed and semi welded PHE, with exceptions provided in this table: 36 36
Basic Components of a Brazed Aluminum Heat Exchanger Brazed aluminum plate-fin heat exchangers (BAHX) are frequently used in low temperature gas processing service Applications: Deep NGL recovery Nitrogen rejection Air separation units Helium recovery LNG production Refrigeration Plate Fin Exchanger (BAHX) Composed of alternating layers of corrugated fins and flat separator sheets called parting sheets Each fluid pass in a core has the appearance of a section of the wall of a cardboard box Number of layers, type of fins, stacking arrangement, and stream circuiting will vary Plate-Fin Heat Exchanger (Courtesy Chart Heat Exchangers) 37 37
BAHX Advantages and Disadvantages Advantages Compact, lightweight and efficient (25 times more surface area per unit weight than an equivalent shell and tube exchanger) Can combine multiple fluids and duties (cold box) Cost effective, especially for clean gases and light hydrocarbon liquids Minimum design temperature is 4 K [-269 C, -452 F] Can achieve temperature approach of 1 C [2 F] Core and Kettle Exchanger Advantages over shell and tube exchangers: Significantly higher heat transfer surface area per unit volume Temperature approaches of 1 C [2 F] Used as chillers and condensers in gas processing and LNG plants with boiling refrigerant as the cooling medium Disadvantages Mechanical cleaning difficult/impossible Mercury corrosion Vulnerable to fire Maximum pressure 100 barg [1450 psig] Limited size Vulnerable to temperature cycling fatigue Complex design procedure (Courtesy Chart Heat Exchangers) 38 38
Printed Circuit Exchanger (PCHE) Stacked Plates Printed circuit exchangers (PCHEs) were introduced in the oil and gas industry in the early 1980s PCHEs are constructed from flat metal plates into which flow channels have been milled or chemically etched Passages are typically 1-2 mm [0.04-0.08 in] deep Two or more fluids can be accommodated in the core Diffusion bonding is a welding process in which the plates are compressed together and heated to just below the melting temperature of the material Printed Circuit Heat Exchanger To complete exchanger construction, fluid headers and nozzles are welded to the core to direct the fluids to the appropriate passages Design pressures are very high, up to 50 MPa [7280 psig] The most common service for PCHEs are discharge coolers and gas-to-gas exchangers in offshore environments (Courtesy Heatric) 39 39
PCHE Advantages and Disadvantages Advantages Compact, lightweight & efficient Size and weight < 25% of shell and tube heat exchanger Good for very high pressure 700 bar and clean, nonfouling fluids No pressure relief required Disadvantages Small (2 mm) flow passages so plugging can be an issue Cannot mechanically clean Not suitable for high viscosity liquids Susceptible to thermal stress failure in temperature cycling services Finned Tubes and Pipe-in-Pipe Heat Exchangers This pipe-in-pipe exchanger may be advantageous for relatively low heat loads, where one stream is a gas or viscous liquid or for relatively small exchangers operating at high pressure Single Tube with Fins Multi-Tube with Fins All fins shown are on the outside of the tubes, but they also can be used inside the shape and style vary widely 40 40
Pipe-in-Pipe Advantages and Disadvantages Advantages True counter-current flow Good for viscous liquids Good for high pressure Can easily be enlarged or reduced in size by adding or removing a single tube unit Disadvantages Limited in size, good for small heat loads Fins increase P, difficult to clean Pipe-in-pipe exchangers are configured such that the fluid s flow is true counter-current The upper economic limit of these exchangers is a UA of 79 kw/ C [150 000 Btu/hr- F] With corrosive fluids, erosion-corrosion may be enhanced due to impingement and turbulence problems Examples of Coil Wound Heat Exchangers Very popular for LNG service Minimum resistance to flow Maximum surface area per unit weight and volume Manufactured from aluminum Multiple tube bundles to handle several fluids (Courtesy Linde Engineering) 41 41
Indirect Fired Heaters Typically a fire tube heater in which the fire tube is immersed in heat transfer fluid Process fluid circulates through a second heat transfer coil immersed in the heater transfer fluid Water bath - applications < 100 C [212 F] Natural gas line heaters and natural gas heaters upstream of pressure let-down stations Molten eutectic salt bath > 260 C [500 F] Regeneration-gas heaters in small dry-desiccant dehydration systems Crude oil and condensate stabilizer reboilers Example of an Indirect Fired Heater Used to heat oil and gas in production operations, where the heat loads are not large 42 42
Primary Applications of Fired Heaters Direct Fired Heaters (Q = 3 to 100 MW [10 to 340 MMBtu/hr]): Combustion in a fire box, process fluid flows through the tubes Typically used in high heat duty applications Boilers Still bottom heaters in lean-oil plants Regeneration-gas heaters in dry-desiccant dehydration systems Hot oil (or other heat transfer fluid) heaters Oil heaters upstream of oil dehydration units Crude oil or condensate stabilizer reboilers Combustion in a fire tube usually immersed in the process fluid Typically used in smaller heat duty applications Small boilers Glycol reboilers Heater treaters in oil dehydration applications Reboilers in small amine systems Common Direct Fired Heater Types in Oil and Gas Processing 43 43
Learning Objectives You are now able to: Describe compact heat exchangers and fired heaters 44 44
6/14/2017 Learning Objectives Heat Transfer Equipment Overview Core Process Cooling Methods and Air-cooled Heat Exchangers (ACHE) By the end of this lesson, you will be able to: By the end of this lesson, you will be able to: List the four primary process cooling (heat rejection) methods Describe why air-cooled heat exchangers are so frequently used, key operating parameters, and the difference between induced draft and forced draft designs 45 1
6/14/2017 Process Cooling In all processes, heat must be rejected to ambient (heat sink) Methods: 1. Once-Through Cooling Water (Direct Cooling) 2. Cooling Towers 3. Indirect Heating Medium 4. Air-Cooled Heat Exchangers (ACHE) Applications include: 1. Compressor aftercoolers 2. Refrigeration condensers 3. Reflux condensers 4. Steam condensers PFD of a Direct Cooling Water System Used in offshore facilities and onshore facilities located near a large body of water, e.g. sea, lake, river, et. al. 46 2
6/14/2017 Advantages and Disadvantages Once-Through Cooling Water Heat Sink Temperature: water ambient temperature Heat Transfer Fluid: water Approach: 5-10 C [9-18 F] (process fluid to heat sink temperature) Advantages: 1) Simplicity, low capital cost 2) Typically gives lowest process temperatures 3) Water is heat transfer fluid 4) Exchangers are small, minimizing footprint 5) Water is less susceptible to ambient temperature fluctuations 6) Less equipment than an indirect cooling system 7) Potentially lower CAPEX than indirect systems, especially for only a few cooling loads Disadvantages: 1) Limited availability, e.g., desert applications 2) Temperature limits on water returned to environment 3) Water is usually corrosive and fouling, this can be a significant problem for systems that use sea water 4) Freezing 5) Water can be contaminated by process fluid creating environmental discharge issues 7) Low sea water temperature may cause hydrate problems in the process 8) Sea water systems require corrosion resistant metallurgy, which is often titanium PFD of an Indirect Cooling Medium System Used in offshore facilities 47 3
6/14/2017 Advantages and Disadvantages Indirect Cooling Medium Heat Sink Temperature: Ambient water temperature Heat Transfer Fluid: Ambient water Approach*: 3-5 C [6-9 F] on ambient water / water heat exchanger Approach*: 5-10 C [9-18 F] on process heat exchangers Advantages: 1) Less equipment exposed to ambient water, which is corrosive and fouling 2) Allows a wider range of heat exchanger options 3) Allows the use of less aggressive cooling medium, such as glycol / water mixtures 4) Less susceptible to ambient temperature fluctuations Disadvantages: 1) Requires additional larger heat exchanger and circulation pumps 2) Environmental limits on temperature of ambient water return 3) Sea water / water can be contaminated with indirect cooling medium 4) Freezing in some locations * process fluid to heat sink temperature PFD of a Cooling Tower System Make-up Water Warm Water Return Air Blowdown Cooled Water to Process Cooling towers are seldom used in oil and gas processing applications Large supply of ambient water is not necessary 48 4
6/14/2017 Advantages and Disadvantages Cooling Towers Heat Sink Temperature: wet-bulb air temperature Heat Transfer Fluid: water Approach*: 15-20 C [27-36 F] Advantages: 1) Water is heat transfer fluid 2) Exchangers are small, minimizing footprint 3) Large supply of ambient water not necessary 4) Lower process temperatures achievable than air cooling Disadvantages: 1) High capital and operating cost 2) Make-up water supply required 3) Chemicals are necessary to treat water for corrosion, scaling, algae, etc. 4) Cooling water blowdown disposal 5) Freezing * process fluid to heat sink temperature The Two Basic Types of ACHEs ACHE are the most popular in onshore facilities Offshore, ACHEs are sometimes used on shallow water installations but are seldom if ever used in deeper water (Courtesy the Rainey Corp.) 49 5
6/14/2017 Induced Draft versus Forced Draft Induced Draft Forced Draft The tube bundle is covered The air plenum chamber is above tube bundle The fan is above the tube bundles (Courtesy the Rainey Corp.) Induced Draft and Forced Draft Air Coolers The tube bundle is not covered The air plenum chamber is below tube bundle The fan is below the tube bundle 50 6
6/14/2017 ACHEs Advantages and Disadvantages Advantages 1. Air readily available everywhere 2. Low environmental impact 3. Lower maintenance than cooling towers 4. Less fouling than water 5. Mechanically simple and flexible 6. Partial cooling available in the event of power failure 7. Facility water consumption requirements reduced ACHE Key Operating Parameters Type of ACHE Induced or Force Draft Process fluid Vapor or liquid coolers Condensers Properties Overall heat transfer coefficient Disadvantages 1. Highest heat sink temperature compared to other methods 2. Large footprint and equipment size 3. Process fluid freezing in low temperature environments 4. Air flow must be free of surrounding obstructions 5. Fan noise 6. Daily temperature variation affects ACHE performance 7. More complex control systems required 8. Winterization of equipment is expensive 9. Thermal cycling must be limited Air ambient temperature, atmospheric pressure and relative humidity Air flowrate Tube design and number of bays Type of tube fins Fan arrangement, type and speed Control of cooled fluid temperature 51 7
6/14/2017 Heat Exchangers Specification and Selection These are some factors you should consider: 1. Do not specify or purchase a heat exchanger without consideration of its effect on the total process. 2. Do not make the capital cost of the heat exchanger a sole criterion for purchase. 3. Acquaint the vendor with details of service and point out the choice will be made on both initial and operating cost, not initial capital cost alone. 4. Use realistic pressure drop specifications since this affects size and cost. Allow as much pressure loss as economics dictates for the actual system and not merely reproduce a standard spec that might not apply. 52 8
Learning Objectives You are now able to: List the four primary process cooling (heat rejection) methods Describe why air-cooled heat exchangers are so frequently used, key operating parameters, and the difference between induced draft and forced draft designs PetroAcademy TM Gas Conditioning and Processing Core Hydrocarbon Components and Physical Properties Core Introduction to Production and Gas Processing Facilities Core Qualitative Phase Behavior and Vapor Liquid Equilibrium Core Water / Hydrocarbon Phase Behavior Core Thermodynamics and Application of Energy Balances Core Fluid Flow Core Relief and Flare Systems Core Separation Core Heat Transfer Equipment Overview Core Pumps and Compressors Overview Core Refrigeration, NGL Extraction and Fractionation Core Contaminant Removal Gas Dehydration Core Contaminant Removal Acid Gas and Mercury Removal Core 53 51