bhe install

8/13/2019 BHE Install

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Brazed Heat

Exchanger

Installation Manual


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I. Introduction

The Brazed Plate Heat Exchanger

Alfa Laval is credited with

inventing the original brazed plate heatexchanger. The brazed heat exchanger

is a compact variation of the traditionalplate heat exchanger. But, unlike the

traditional plate heat exchanger, the

BHE does not have a carbon steel frame,gaskets, tightening bolts or carrying bar.

It consists simply of AISI 316 stainless

steel corrugated channel plates, apressure plate and a frame plate with

connections that are brazed together in a

vacuum furnace.

How It Works

When the plate pack is

compressed, it creates a continuousseries of channels with portholes in each

of the four corners. The media enters

the inlet connections and is distributedinto the narrow channels between the

plates. The passages between the plates

and corner portholes are arranged so thatthe two heat-transfer media can travel in

alternate channels. A brazed seal around

the outer edge of the plates retains themedia within the channels. As the

warmer medium passes through the unit,

it releases heat energy to the thin plate

wall, which instantly transfers it to the

colder medium on the other side.The thin plates have a uniquely

designed herringbone geometry that

creates high turbulence and low pressure

loss. This optimal plate pattern gives theBHE and extremely high overall heat

transfer coefficient. This pattern has

been developed through theoreticalcalculations, checked by laboratory tests

and proven itself in the field.

II. The Alfa Laval Brazed

Heat Exchanger Series

The Copper-Brazed Heat Exchanger Line

Alfa Laval has developed astandard line of BHEs to encompass

different applications and heat loads.

These heat exchangers, from the smallestunit, the CB14, to the largest, the

CB300, are brazed with 99.9% pure

copper.

The Nickel Brazed Plate HeatExchanger is an alternative for

applications where copper is not

appropriate, such as de-ionized water orammonia.

Brazed Heat Exchangers aresuitable for liquid/liquid, steam/liquid,

and gas/liquid applications.

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Standard BHEs

Custom-designed BHEs can be

equipped with:

Multiple passes

Different connection positions Non-standard connections

Three-media configurations

Multi-pass BHEs

Multi-pass units are used to

increase the thermal length of the heat

exchanger. With this design, more heat

is transferred from the hot medium to thecold medium, at the expense of a higher

pressure drop. Figures 3A and 3B

illustrate the difference between the oneand two pass design.

III. BHE Specifications

Fluid Quality

To minimize risk of corrosion,the media pH values should be neutral.

The media must not contain chemicalscorrosive to stainless steel (AISI 316) or

the brazing material (copper or nickel).

Stainless steel is especially sensitive tolocalized spot and crevice corrosion due

to chloride, sulfite and sulfate ions.

Above a critical ion concentration thepassivity of the steel breaks down and

local spot corrosion occurs.

Materials Plates and connections AISI 316Brazing material

CB units Copper 99.9%NB units Nickel Alloy

ApprovalSweden Statens Anlaggningsprovning (SA)

Germany Technische Uberwachungsverein

USA Underwriters Laboratories (UL)American Society of Mechanical

Engineers (ASME) upon request

for some modelsCanada Canadian Standards Association

(CSA)

The data label shows:

1) Alfa Laval manufacturing number

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2) Connection position. S indicates

the front cover plate, T the backcover plate.

3) Unit description as follows:

a. Model

b. Plate number and typec. Connection configuration code

Example: CB26-70H S52

CB26 Model Type70 Number of Plates

H Type of Plate in Model

S52 Connection Code

BHE Connections

BHE connections are available inthe following:

Threaded and/or soldered

Flange (some models)

Rotolock

Victualic

For further details, please refer to theBrazed Plate Heat Exchanger Product

Catalog(Pub. No. ENSR00005EN 0207).

IV. Installation

General Information

For the highest heat transfer,

connect the unit so that a countercurrentflow is obtained.

Installation

Figure 5 shows the installation of

an evaporator. For evaporators connectthe refrigerant to the side with the

soldered connections (S3, S4) so that it

enters the unit at the bottom. Theexpansion device should be positioned

not less than 6-8 inches from the

connection (S3). Bent tubes and elbows

between the expansion device and theconnection should be avoided. Connect

the liquid to that side of the BHE that

best suits your installation (S1, S2) or(T1, T2).

NOTE: Units with the option of the

real double circuit have a single water

circuit with connections in a central

position and two independentrefrigerant circuits. The refrigerant

circuits, unless otherwise indicated,

have diagonal flow. The refrigerant

side connections follow the normal

rules with the additional note of being

diagonally opposite.

Mounting

Always mount the unit vertically

in two-phase applications. For single-phase applications the BHE can be

mounted horizontally or verticallywithout affecting the function.

Units smaller than CB26-30 can

be mounted directly on the pipes. Mountlarger units on anti-vibration plates or

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fasten with steel clamps (Figure 6 or 7)

or stud bolts, when included. If there is

risk of vibrations, use an anti-vibrationdevice as in Figure 8. Models with HX,

MX, LX plate configurations or model

AC must not be installed upside down.

The tightening torque for the 5/16 studbolts is 90-105 in-lb; for the 3/8, it is

195-221 in-lb. For larger sizes of units,removable feet and lifting lugs can be

provided as an option.

Threaded Connections

Connect the pipe using adynamometric wrench respecting the

indicated limits. The limits are

measured on the largest diameters. Incase of smaller connections, the torque islower. In the AC units, the Victualic

type connection can be supplied.

To avoid damaging the threadedconnections, it is important to mount the

BHE on the pipes within the

recommended design limits. (See table

below.) (See Figure 9.)

Table: Design Limits

BHE size T(lb) F(lb) MB(ft-lb) Mv(ft-lb)

CB14 3330 1800(-1350) 27 125

CB26,CB52

5550 2160(-1660) 45 285

CB76,AC120,

AC13024950 6070(-4720) 545 740

AC250 30800 7420(-5620) 675 2140

Soldered and Welded Connections

The temperature must not exceedthe melting point of the brazing material.

Use a wet towel around the connection

and the plate pack to reduce the heattransferred to the BHE plate pack during

installation.

Filling material: 30-55% silver alloy

Flux material: Black Flux for silversoldering

1. Clean the soldering assembly surface

at the copper tubes and BHEconnections.

a. Remove oil or other buildup with

degreasing solventb. Polish the surfaces to remove

oxides.

2. Apply the flux to the surface with abrush to remove and prevent

oxidation.3. For refrigeration installations, use a

dry Nitrogen gas on the refrigerantside to prevent oxidation.

4. Heat the soldering area to the

soldering temperature of about

1200F. (Higher temperatures will

melt the brazing material.) Use a

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wet cloth to minimize the heating

zone. WARNING: Unnecessary heating

(above 1200 F) can melt the brazing

material!

5. Keep the tube in a fixed position and

add the filler material.

V. Regulation

The efficient design of plate heat

exchangers allows the total hold-up

volume of the system (pumps, valves,piping and controls) to be much smaller

than that of systems using conventional

heat exchangers. This high efficiency

results in a quick response time. Thevalve and regulation equipment should

be designed accordingly.

The valve with the shortestresponse time should be placed close to

the outlet. This will give a faster

response when there is a small load.Follow the instructions from the valve

manufacturer and, if possible, use a PI

regulator with a logarithmic response.This is especially recommended in steam

applications.

Welding

1. Prepare the edge of the tube for

welding with a 30bevel.2. Place the piping into the connection.

Excessive cycling amplitude of

pressure and temperature can lead to

leakage after some time as a result offatigue phenomena. Thermal dynamicstresses are caused by large fast

temperature changes (more than 50F)and can damage the BHE. An ON/OFF

valve that causes pressure pulsation in

the BHE must be avoided. To minimizethermal fatigue, it is especially important

to avoid pressure and temperature

pulsations in steam applications orchanges in the condensate level inside

the steam condenser.

3. TIG-weld or MIG-weld the tube to

the connection, filling the groove

formed by the two edges. Thismethod minimizes the heating zone.

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Shut Down

VI. Operation Consult system instructions todetermine which pump should bestopped first.A liquid in motion in a pipe

system generates a high level of energy.

When a valve is closed or opened,causing the fluid to stop or continue, it

must be done slowly to avoid shockingthe system.

SLOWLY, close the valve

controlling the flow rate of the pumpbeing stopped.

When the valve is closed, stop the

pump.

Repeat for the other side.

WARNING: Do not use fast-closing

valves unless the pipes of the system

are very short!

If for any reason the heat exchanger

is shut down for a long period, itshould be drained. If the media

processed is corrosive, contains

particles, or has a tendency tocoagulate, it is recommended that the

heat exchanger be rinsed with waterand dried to avoid damage.

Start Up

Note: Consult equipmentmanufacturers start-up procedures forrefrigeration applications.

VII. Freeze Protection Before starting any pump, consultthe system instructions to determinewhich pump should be started first. For freeze protection use

thermostats and/or temperature controlsin the connections opposite to the liquid

inlet/outlet, if any, or in a temperature

pocket close to the outlet.

Make sure the control valve betweenthe pump and the unit is closed.

If there is a valve at the exit, make

sure it is completely open.

Open the vent.Connect the water side pipes toensure that the whole unit runs filled

with water.

Open the valve SLOWLY.

Close the vent after all of the air is

let out. To minimize freezing risk: Repeat the procedure for the other

side of the heat exchanger.1) Use a filter


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Insulation

Airtight insulation isrecommended. It is necessary when theunit is working as an evaporator at low

temperatures. This can be made, among

other solutions, using insulation sheets(Armaflex or similar) cut into

appropriate sizes and glued together as

shown. (See Figure 11.)

VIII. Maintenance

Heat Transfer

The purpose of the BHE is totransfer heat from one medium to

another. Heat passes very easily through

the thin walls separating the two media.

The pattern pressed into the plates makesthe plates strong and rigid and increases

the rate of heat transfer. This high rate

of heat transfer can be inhibited by the

formation of deposits on the platesurfaces. The corrugated pattern on Alfa

Laval plates induces turbulent flow.Turbulence provides strong resistance to

deposit buildup, but it cannot always

eliminate fouling. The deposits mayincrease the total wall thickness, and

consist of materials of a much lower

thermal conductivity than of the metal

plate. Thus, a layer of deposits canseverely reduce the overall heat transfer

rate. Corrosion can also occur under the

deposits. For corrective action, please

see Cleaning below.

Pressure Drop

Pressure drops are wasted

energy. All pipe systems, andequipment included in them, offer

resistance to the media flowing through

them. Some pressure drop is inevitable,

but it should be kept as close as possibleto the designed value for the BHE. The

formation of deposits on the heat transfersurfaces reduces the free space betweenthe plates. This means that more energy

is required to achieve the desired flow in

the BHE. Large particles and fibers mayalso clog the heat exchanger if it is not

equipped with a strainer. A reduced

ability to maintain the desired

temperatures along with an increasedpressure drop on either media, are

symptoms of fouling or clogging. For

corrective action, please see Cleaningbelow.

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Cleaning

Clean with detergents for fatty

deposits. For heavier fouling usechemicals such as formic acid, citric

acid, vinegar, or other organics in

concentrations compatible with copper.Alfa Laval BHEs can be cleaned

in place with the Cleaning-in-Place

(CIP) system, which chemically removescalcium deposits and other forms of

scaling from plate surfaces (See Figure

12.) Different solutions can be used,depending on the type of deposits. Every

application has to be considered

separately. The Cleaning-in-Place

procedure is generally the same,

regardless of the solution used.

CIP Procedure

1. Drain the unit.

2. Rinse with fresh water.3. Drain water.

4. Fill with fresh water.

5. Add cleaning agent (solution andconcentration depending on type of

fouling).

6. Circulate the cleaning solution (iffeasible).

7. Drain the cleaning solution.8. Add and circulate the passivating

liquid for corrosion inhibition of

plate surfaces.9. Rinse with fresh water.

10. Drain.

CAUTION: Do not use liquids that

are corrosive to stainless steel or the

brazing material (copper or nickel)!Do not leave the unit on standby after

cleaning! Contact the Alfa Laval

Service Center (1-866-Alfa Laval) for

more information about cleaning-in-

place equipment, detergents or

service.

IX. Assistance and Field

Service

TroubleshootingTo assure correct performance of

the unit, please check that:-it is correctly connected according

to page 4 of this leaflet.

-it is absolutely clean and free fromdeposits. Increased pressure drops

can reveal fouling.

-the control equipment is correctly

set up and that freezing does notoccur.

Alfa Laval maintains a largehighly specialized engineering staff tohandle your questions and problems.

Your nearest Alfa Laval representative

will be happy to provide you with quotesor answer to your questions. To assist

your representative in finding the best

solution, please provide the following

sizing information along with yourinquiry:

Hot Side Cold Side

FluidMass flow

Temperature InTemperature Out

Maximum Pressure Drop

Design Pressure

For Refrigeration Applications

Condensing TemperatureEvaporator Temperature

TX Valve Superheat

Total Heat of Rejection

Total Evaporator Tons

GPM

F

F

psig

psig

F

F

F

kBTU/H

TR

GPM

F

F

psig

psig

F

F

F

kBTU/H

TR

If you do not have this

information, it may be sufficient todescribe the existing heat exchanger.

bhe install

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