Process Engineering Equipment Handbook Episode 2 Part 6 potx

Heat Pumps; Heat Pumps, Geothermal; Heating Systems with a Renewable Energy Source* Working Theory behind Geothermal Heat Pumps How earth loops work A system of high-density polyethylen

G-14 Generators; Turbogenerators

FIG G-11 Open cooling system (Source: Alstom.)

G-12 Generator assembly (Source: Alstom.)

Pilot exciter

The pilot exciter is a synchronous generator with permanent magnets on the rotor.The rotor magnets are enclosed in a short-circuited aluminum ring that preventsdemagnetization of the poles because of short-circuiting in the stator winding.The stator winding insulation satisfies the requirements for temperature class F(155°C)

of a split seal of oil-resistant insulation material An air extractor is connected tothe bearing space to prevent oil leakage through the external seals Internal shaftseals are provided with sealing caps and the intermediate space is connected to theblocking air from the pressure side of the fan

Generators; Turbogenerators G-15

FIG G-13 Main exciter (Source: Alstom.)

The exciter can be provided with either an open or a closed cooling system.With an open cooling system, a housing with filter cassettes is mounted on oneside of the exciter housing for the incoming cooling air The cooling air exit isdirected downward under the exciter housing

With a closed cooling system, the filter housing is replaced with supply andexhaust air channels connected to the cooler housing of the generator

Surface Treatment

In its standard version, the generator is painted with a lacquer of two-componenttype based on ethoxylized chlorine polymer The generator is primed inside andoutside and then finished externally in a neutral blue color The paint is resistant

to corrosive, tropical, and other aggressive atmospheres

The sliprings are manufactured of steel and have generously dimensioned contactsurfaces for the carbon brushes The spiral-machined contact surface is carefullyground and polished This prevents current concentrations and reduces brush andslipring wear The sliprings are shrunk on the shaft extension on a cylinder ofinsulating material The radial connections from the sliprings to the terminalconductors consist of insulated contact screws through holes in the shaft extension.The terminal conductors in the slipring shaft and the rotor shaft are connectedwith contact screws

The carbon brushes in the handle parts are mounted in holders of coil-spring typethat give a constant brush pressure during the service life of the brush The handleparts are insulated and the brush holders can be removed from the brush holderpockets by hand when the brushes are to be replaced Brush replacement is thuspossible during operations

Slipring housing

Openings are formed in the side walls of the housing for service These are coveredwith hatches provided with air filters The opening in the end wall of the housing,

G-16 Generators; Turbogenerators

towards the generator, through which the slipring shaft passes, is provided with aseal.

Inspection and Testing

General basic inspection and testing points performed during the fabrication of thegenerators are included in a check plan Each manufacturing operation is subject

its result is used as a reference for the subsequent machines of the same type Amore extensive test can be offered separately.

Control and Protection

Temperature monitoring

A number of platinum wire resistance elements installed in different parts of the machine are used for continuous monitoring of the temperature of the parts.The connection cables of the elements are routed to junction boxes on the outside

of the stator housing The number and location of the elements are shown in thefollowing list:

G-18 Generators; Turbogenerators

FIG G-15 Slipring assembly detail (Source: Alstom.)

Number Location

As a standard, the resistance elements have a resistance of 100 ohms at 0°C

Bearing vibration measurement

Vibration transducers of seismic type for bearing vibration measurement can bedelivered mounted on the bearing shields of the generator

 Negative phase-sequence current protection

 Stator earth fault protection

 Rotor earth fault protection

 Underexcitation protection and/or underexcitation limiter

 Reverse power protection (depending on the drive machine type)

Generators; Turbogenerators G-19

TABLE G-1 Normal Testing

Measurement of generator losses (through run-down test) ¥

Loading point with cos j = 0 overexcited ¥

 Overexcitation and/or overexcitation limiter

 Loss-of-excitation protection; in installations where there is a risk of highovervoltages, a surge diverter is to be installed and, in certain cases, protectivecapacitors

Operating Characteristics

Operations with constant winding temperature

With gas turbine operations, the principle described as follows is applied Thisprovides an optimum relation between the permitted power output of the generatorand the power available from the turbine at varying cooling medium temperatures

In accordance with international standards, particularly for gas turbine–poweredgenerators, the generator can be loaded so that the maximum winding temperaturepermitted remains the same with a cooling air supply temperature other than 40°C The winding temperature rises permitted increase or decrease as much asthe temperature of the cooling medium falls below, or exceeds, respectively, thevalues given previously

Synchronous compensator operation

The generators are particularly suitable for synchronous compensator operation Topermit such operation, however, mechanical disconnection of turbine and generator

is usually required and one of the main bearings must be provided with thrust bearings

Operation at low ambient temperatures

With very low temperatures the generator can be provided with a recirculationarrangement for cooling air or water

Noise Reduction

When there are special acoustic requirements, the generator can be installed in asound-absorbing enclosure consisting of a steel frame with panels of perforated steelsheets with sound-absorbing mineral wool in-fill

The sealing against water leakage between the panels and the supportingstructure consists of a self-adhesive rubber strip and silicon-rubber caulking.The roof and walls of the enclosure are provided with service openings

Base frame

The stator frame of the generator is self-supporting and therefore requires no baseframe to provide stiffness If the center height is required to be higher thanstandard, the generator can be provided with a separate, welded, steel base frame

Grinding (see Abrasives; Some Commonly Used Specifications, Codes, Standards,

and Texts)

Grinding Wheels (see Abrasives)

G-20 Grinding Wheels

Hazards (see Color Coding; Explosion; Some Commonly Used Specifications,

Codes, Standards, and Texts)

Heat Exchangers (see also Cogeneration; Regenerator; Vaporizers)

A heat exchanger basically removes or adds heat to a fluid The most common types

in process plants are shell and tube exchangers Plate types (consisting of conducting fins), cascade types (single pipe bent back and forth many times), andspiral plate and extended surface types are less common The working principle

heat-behind the heat exchanger is well illustrated in the section on condensers (see

Condensers) A heat exchanger is usually custom designed for a large process plant

by the overall contract designer Builders of items such as condensers andseparators generally also make related items such as heat exchangers and will have

a catalog on smaller items that can be bought without a custom order

Some information on different commonly available heater types follows

Heat Pumps; Heat Pumps, Geothermal; Heating Systems with

a Renewable Energy Source*

Working Theory behind Geothermal Heat Pumps

How earth loops work

A system of high-density polyethylene pipes is buried in the ground or installed in

a body of water to exchange heat between the building and earth An antifreezesolution is circulated through the pipes by low wattage pumps The plastic pipe wallbecomes a heat exchanger between the fluid and the surrounding earth In theheating mode the liquid in the pipe is cooler than the surrounding earth In thecooling mode the opposite condition exists Since heat flows from a warm area to acooler one, heat exchange occurs under both conditions

Pond and lake loops

Short polyethylene loop coils are stretched horizontally and attached to a plasticmesh to form a mat-style anchored heat exchanger Several mats are connectedtogether, and once in position the pipes are filled with fluid, possibly weighted, andthe mats sink to the bottom See Fig H-1

Open loops (well systems)

In areas where a good supply of clean ground water and an accessible waterdischarge system is available, an earth loop becomes unnecessary Well water ispumped directly through the unit and heat is either extracted from or rejected back

to the water table See Fig H-2

H-1

* Source: Enertran, Canada Adapted with permission.

Earth loop configurations

Earth loops (Figs H-3 and H-4) are installed in either horizontal or verticalconfigurations; the choice depends upon geographical location and the land areaavailable [This information source’s systems are sized to meet or exceed CSAStandard—M445 (sizing requirements), fulfilling the stringent energy efficiencyrequirements of the North American Building Codes.] Earth loop lengths arecalculated using a sophisticated computer program that predicts annual loopperformance, energy consumption, and operating costs

Horizontal loops. Horizontal loop designs vary from a single, in-series pipe tomultipipe parallel systems Pipes are laid in trenches 4–6 ft deep, using a backhoe

or trencher, and pressure tested, and then the trench is backfilled See Fig H-3

Vertical loops. Vertical loops usually require less pipe than horizontalconfigurations Vertical loops are connected in series or parallel or both Drillingequipment produces small diameter holes, 75 to 300 ft deep Two pipes are joined

H-2 Heat Pumps; Heat Pumps, Geothermal; Heating Systems with a Renewable Energy Source

FIG H-1 Pond and lake loops (Source: Enertran.)

FIG H-2 Open loops (well systems) (Source: Enertran.)

with a U-bend and are inserted into each hole Once inserted, the pipes are pressuretested and the bore hole is backfilled See Fig H-4.

Partial hot water (PHW) heating

The PHW heating option transfers excess heat produced by the unit into anydomestic hot water tank, whenever the system is operating Savings of up to 65percent per year are possible with PHW

Heat Pumps; Heat Pumps, Geothermal; Heating Systems with a Renewable Energy Source H-3

FIG H-4 Vertical loops (Source: Enertran.)

FIG H-3 Horizontal loops (Source: Enertran.)

On-demand hot water (ODHW) heating

This heating option transfers heat into hot water on demand, at any time it isrequired ODHW is suitable for heating swimming pools and spas, or in-floorheating in combination with a forced air heating and cooling system

Liquid-cooled air conditioning

Operating at approximately 50 percent less than the cost of traditional airconditioners, including very low flow rates (1 US GPM per ton), liquid-cooled airconditioners can transfer heat from a building into a liquid heat sink—such asdomestic hot water, swimming pools, commercial laundries, ground water, or anearth loop They can be retrofitted to most central forced air systems, or used forspot-cooling in difficult applications All components are installed inside thebuilding, reducing maintenance service cost and installation cost Liquid-cooled airconditioning systems eliminate the need for potentially noisy outdoor condensers.See Fig H-5

High humidity conditions

Excessive humidity can cause major structural damage if left unattended for longperiods of time High humidity also accelerates the growth of mold, bacteria, andviruses Indoor swimming pools, spas, and commercial operations such as indoorice rinks and underground pumping stations, all depend on good humidity control

In a situation where dehumidification is needed and heat is needed in other areas, various heat transfer methods, including dehumidification, as well assimultaneously transferring the process heat to water/air, can be used

Mechanical dehumidification systems

Dramatic savings on the energy cost of dehumidification, compared to conventionalair makeup systems is possible Moist air drawn through the system is cooled belowits dew point, drawing moisture from the air Heat captured by the system is

H-4 Heat Pumps; Heat Pumps, Geothermal; Heating Systems with a Renewable Energy Source

FIG H-5 O perating cost comparison (reflects heating costs only) (Source: Enertran.)

recycled back to the pool enclosure as warm dry air or back into the pool as warmwater Constant positive humidity control ensures comfortable conditions at alltimes These mechanical dehumidification systems can be easily integrated with ageothermal system and other products, including liquid-cooled air conditioning, toprovide economical air conditioning.

Hybrid systems

Hybrid systems combine the highest efficiency, liquid cooled air conditioning with

an integrated hot water heated, forced air delivery system in one package Heatsource options can be a hot water heating system, tanks, liquid to liquid heatpumps, etc Cooling options are identical to those used for liquid cooled airconditioners (See Figs H-6 through H-8.)

Reference and Additional Reading

1 Soares, C M., Environmental Technology and Economics: Sustainable Development in Industry,

Butterworth-Heinemann, 1999.

Heat Pumps; Heat Pumps, Geothermal; Heating Systems with a Renewable Energy Source H-5

FIG H-6 Cooling position (Source: Enertran.)

FIG H-7 Heating position (Source: Enertran.)

Heat Treatment (see Metallurgy)

Heaters, Electric*

Impedance-Type Electric Heaters

The advantages of impedance heaters (see Fig H-9) are as follows:

1 Low life-cycle costs

2 Low maintenance cost

3 Long operating life

4 Simple operating cycle

5 Easy to clean—easy access

H-6 Heat Treatment

FIG H-8 Heat reclaim options/opportunities (Source: Enertran.)

FIG H-9 Impedance-type electric heaters (Source: Armstrong Engineering Associates.)

* Source: Armstrong Engineering Associates, USA Adapted with permission.

Heaters, Electric H-7

6 Available in most metals

7 Close and precise temperature control

8 Ideal for heating acids, other corrosive fluids

9 Just the tube is needed—no shell is required

10 High electrical flux density is possible

11 Handles 2-phase mixtures, liquids and solids mixed

12 Suitable for high-temperature (2000°F/1093°C), low-temperature (-325°F/-198°C), and high-pressure (up to 5000 psi/352 kg/cm2) operating parameters

13 Heaters operate at very low voltages so there is no safety issue

14 Flow pipes carry the current and heat the fluid passing through directly

15 Less corrosion due to thicker tubes for same exit temperature of fluid

16 Accurate heat transfer data (in tube flow) allows accurate heater design

How impedance heating works

Electrical connections are secured to each end of the pipe through which the fluidsflow Refer to Fig H-10 for the location of electric terminals on a common single-

FIG H-10 Typical impedance heater 180 kW heating air to 1500°F (816°C) in a U.S chemical plant (Source: Armstrong Engineering Associates.)

phase connected arrangement The pipe’s electrical resistance causes the pipe toheat up and impart heat to the fluid flowing inside the pipe Voltages used for this application are typically relatively low (50 V or below) See Figs H-10 throughH-12.

Heat transfer/pressure drop in impedance heaters

Since the tube wall is hot and the flow is through normal tubes or pipes, the heattransfer is easily calculated by engineers using experience in design and rating ofchemical plant miscellaneous chemical fluids

In Fig H-12, the heater is heating air from atmospheric intake to over 1850°F(1010°C) exit temperature

“Electrofin” Heaters

This information source has designed a specific model of heater trademarked

“Electrofin.” It is a compact design with the following features:

1 Up to 40 kW per single tube in a 20-ft-long (6-m) unit and more surface per tubeoften results in smaller shell diameter (lower cost)

2 Available in most metals including steel, stainlesses, nickel, Monel, Inconel,Incoloy, Hastelloy, etc

3 Single tube or multiple tube combinations; lengths to 20 ft (6 m)

4 Accompanying control panels available with thyristor or contactor designs

5 Design pressures available up to 6000 psi (442 kg/cm2)

6 Fluid temperatures available -292°F to +1202°F (-180°C to +650°F)

7 Suitable for most liquids and gases including high viscosities

H-8 Heaters, Electric

FIG H-11 Single-phase, straight tube impedance heater (Source: Armstrong Engineering Associates.)

See Figs H-13 through H-19.

“Electrofin” tank heaters (see Fig H-20) have an attached thermocouple allowingmonitoring of the heating element that can be connected to a relay in the control

to allow the unit to be shut down if the internal heater overheats due to debris,fouling, etc

Fintube tank heaters can also use steam or other normal heating fluids

H-10 Heaters, Electric

FIG H-14 Two types of single tube heater (Source: Armstrong Engineering Associates.)

FIG H-15 Multitube longitudinal fin tube-type heater (Source: Armstrong Engineering Associates.)

FIG H-16 Three-stage single tube Inconel heater for heating viscous organic fluid (Source: Armstrong Engineering Associates.)

Heaters, Electric H-11

FIG H-17 Twin single tube vapor heaters of stainless steel type 304 construction heating ethyl ether from 392°F (200°C) to 842°F (450°C) (Source: Armstrong Engineering Associates.)

FIG H-18 Heavy-duty electrical resistance heating elements with welded fins (Source: Armstrong Engineering Associates.)

FIG H-19 Robust thick fins are continuously welded to the electrical heating element (Source: Armstrong Engineering Associates.)

Electric Hot Pipe Tank Heaters

This is a heavy robust heater type, strong enough for very high viscosity fluids.Features include:

1 Fins are welded to pipe Strong contact (between fins and pipe) does notdeteriorate with cycling over time as compared to wrapped or unwelded thin fins,which lose heat transfer due to rising contact resistance The heaters do not losecapacity with age Fins are 1.5-mm thick Liberal fin surface gives low wattdensity on heating surface

2 Fins are strong enough to allow high pressure hose cleaning and user walking

6 Relatively simple control available

7 Internal electric heating elements can be withdrawn from the tank withoutdraining the tank while the outer fintube remains in the tank

8 Available in various metals: steel, stainless steels, Monel, Inconel, Incoloy, nickel,Hastelloy, silicon bronze, etc

9 Heaters can be supplied in long lengths Also with bare heating pipes (no fins)

if preferred

Tank Heater Types (Steam or Electric Heated)

See Figs H-21 through H-26

H-12 Heaters, Electric

FIG H-20 Shop photograph of CSA-approved electric hot pipe tank heaters showing terminal boxes of explosion-proof Ex(d) design Serrated fin tube outer pipes The internal heating elements are removable without draining tank (Source: Armstrong Engineering Associates.)

FIG H-21 Suction-type heater, normally installed in tank side nozzle, to heat up relatively larger flows of viscous materials using steam, hot water, or other heating fluid in the tubes These heaters normally have low shell side pressure drops to minimize npsh problems on pumps For very high viscosity fluids, consult the manufacturer for methods of reducing intake viscosity An internal shutoff valve can be used to allow easy bundle removal Main uses of this type heater include bunker C, fuel oils, asphalt, molasses, caustic, etc (Source: Armstrong Engineering Associates.)

FIG H-22 Line-type heater This is simply a suction-type heater with an enclosed end so that the heater can be installed outside the tank This permits addition of an external valve between the tank and the heater to allow servicing of the heater without pumping down the tank Basically, the incentive to use a line heater is either maintenance ease or piping simplicity (Source: Armstrong Engineering Associates.)

H-13

FIG H-23 Bayonet-type stab-in tank heater For installation in side entering tank nozzle Bayonet heaters are usually single pipe, with fins to allow good natural convection circulation of the fluid being heated These heaters are available in a multiplicity of metals, including the stainless steels (Source: Armstrong Engineering Associates.)

FIG H-24 Coil-type stab-in tank heater This type heater is installed through a side entering tank nozzle, and differs from the bayonet type in that usually more pipes or tubes than one are used, requiring therefore a tubesheet and bonnet, or a continuous coil to allow for usually lower flow of heating medium such as heat transfer oils, diphenyl, etc Fins are helical for natural convection (Source: Armstrong Engineering Associates.)

FIG H-25 Vertical cluster “in tank” heater This type of heater can be supplied in many metals but

is usually steel or stainless steel, is used to give very large amounts of surface in a relatively confined space These heaters can be either steam or heat transfer oil heated Very high viscosity fluid application: By placing several such heaters around the intake of a suction heater, the fluid viscosity can be reduced sufficiently to allow the normally highly viscous fluids to enter the suction heater intake, where otherwise they might not flow well enough to ensure normal operation

of the suction heaters (Source: Armstrong Engineering Associates.)

FIG H-26 Horizontal “in tank” heater This type heater has fins to allow good thermosiphon circulation of the fluid being heated, and gives a wide thermal current stimulation Due to the compact surface, much larger amounts of heat can be added to the tank contents than when using bare tube coils of comparable area (Source: Armstrong Engineering Associates.)

Sheathed Element Electric Process Heaters

Design pressures available depend somewhat on bundle diameter but bundles

up to 10 in (254 mm) are available to very high design pressures [up to 10,000 psi(703 kg/cm2)] Heaters are supplied to various codes (ASME, Stoomwezen, mostEuropean, and also Lloyds, etc.) See Figs H-27 through H-31

Design temperatures of this unit are available from cryogenic levels up to about1250°F (677°C) design operating temperature

Most sizes are CSA and BASEEFA approved as well as Australian Code approved.Typical shell diameters run from 1.5 in (38.1 mm) OD up to and including 48 in(1220 mm) OD

Shells and pressure parts are available fabricated of most pressure vesselmaterials (steel, stainlesses, nickel, Monel, Hastelloy, Inconel, Incoloy, etc.)

Design voltages include 600 volts and higher

Connections for sheathed element electric process resistance heaters as well ascircuit equations are in Fig H-32

Heaters, Electric H-15

FIG H-27 Process-type heaters are available from 2 in (51 mm) to 48 in (1219 mm) shell diameter Unit is 42 in (1066 mm) shell diameter (Source: Armstrong Engineering Associates.)

FIG H-28 Bottom bundles are sheathed element heater Liquid level of intermediate fluid is boiled

by bottom bundle and then condenses on top bundle Intermediate unit is used when pressure is very high or upper heating bundle is of very costly metal to avoid having the whole unit of the costly metal or the high pressure design, which is thus confined only to the upper bundle (Source: Armstrong Engineering Associates.)

Controls for Electric Heaters

Controls are thyristor type or contactor type with many variations Panels are

pretested where numerous tests, such as heat rise under load, confirmation of

control functions, RF emissions, waveform photography, etc as may be required,

Special attention is given to heat rejection facilities for tropic or warm zone operations to ensure control elements are not overheated In some cases, airconditioners may be attached to panels to keep cooling close to 122°F (50°C).

Features of explosion-proof control panels

The panel shell (see Figs H-33 and H-34) must be heavily built and capable ofwithstanding, without damage, an explosion inside the box due to combined processfluid and air and must not cause failure or damage to the containment vessel