control de tds

7/31/2019 Control de TDS

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BCS4Blowdown control system



Not to scale

Stop valve

BCV30 blowdown valve(electrohydraulically actuated)

orBCV31 blowdown valve

(pneumatically actuated)

To heat recovery system

or blowdown vessel

DCV2check valve

S11 sensor chamberand CP10 sensor

Cooling water inlet

Coolingwateroutlet

Sample outlet

SCS20sample cooler

system (optional)

The BCS4 blowdown control system

How the BCS4 system worksThe BCS4 blowdown system works by periodically

opening the blowdown valve in order to purge the

pipework and set up a flow of boiler water past the

sensor. To avoid wasteful blowdown, especially whilst

a boiler is on stand-by or low load, the system can be

wired to purge every half hour of boiler firing. The

controller measures the electrical conductivity of the

boiler water which is closely related to the level of total

dissolved solids (TDS). This measured value is

compared with the set point in the controller. If it is

lower than the set point the blowdown valve closes at

the end of the purge time and remains closed. If the

measured value is higher than the set point the

controller continues to blow down until the measured

value drops below the set point.

The controllers give indication of the blowdown status,

and have a manual purge facility.

The system is easy to calibrate and commission and

the set point can be quickly adjusted.2

Boiler



The DS1000 is an optional remote

digital display unit

The requirement for blowdownBoiler feedwater can contain a high level of dissolved

solids, even if a feedwater treatment plant is installed.

Water treatment can chemically modify the form of the

dissolved solids, but will not usually remove them

completely, and can even increase the total dissolved

solids (TDS) level.

As steam is evaporated, the TDS level increases in

the boiler water. If the TDS is allowed to get too high

then carryover of the boiler water with steam will occur.

This can cause serious damage to the steam and

condensate systems through waterhammer, corrosion,

and deposits on heat transfer surfaces.

Deposits in control valves and steam traps can build

up rapidly, causing operating problems. Product

contamination and reduced heat transfer rates may

affect productivity.

In order to limit the TDS to the level recommended by

the boiler maker it is normal practice to periodically

drain off, (or 'blow down') boiler water and allow it to

be replaced by relatively low TDS feedwater. Excessive

blowdown is of course very expensive in terms of lost

energy and water treatment chemicals.

Deciding on theboiler water TDS

Conventional shell boilers are normally operated with

the TDS ranging from 2 000 ppm to 3 500 ppm. These

TDS levels should ensure that reasonably clean and

dry steam is delivered to the plant, providing that:

n The boiler is operating near to its design pressure.

n The steam load conditions are not too severe.

n Other boiler water conditions are correctly controlled.

The boiler manufacturer usually recommends a ppmor µS/cm figure.

User benefitsl Accurate TDS level control minimises blowdown.

l Easy to clean sensor.

l Simple retrofit installation.

l Reduces carryover of boiler water with steam.

l For boiler pressures up to 32 bar g.

l For blowdown flowrates up to 11 000 kg/ h

at 32 bar g.

l Automatic control decreases need for

supervision.

The BCS4 system is available

with one of three types of controller:

The wall mounted BC3200

The panel mounted BC3210

The DIN rail / chassis

plate mounted BC1100

3



The controllers

The BC3200 is a wall mounted controller with 4 digit

LED display and two push buttons for simple

commissioning, calibration and operation.

Features include:-

n 230 V or 115 V (50 - 60 Hz) supply, selected by an

internal switch.n Selectable ranges (ppm or µS/cm), to suit all types

of boilers.

n Four digit LED display of TDS (as well as system

status e.g. blowing down or probe cleaning in

operation).

n High TDS alarm relay output, which may be wired

to give remote indication.

n 4 - 20 / 0 - 20 mA output.

n Automatic probe cleaning circuit, (UK patent

No. 2276943), which allows the system to maintain

its accuracy even when some boiler scaling is

taking place.

n Remote display option using DS1000.

n Electronic filtering to give more representative TDS

measurement under high turbulence conditions.

n Selectable security feature to prevent unwanted or

inadvertant changes to settings. (Settings can still

be viewed, but not altered).

n An optional front cover lock is available.

The BC3210 has exactly the same features as the

BC3200, but has an enclosure suitable for mounting

in a boiler panel. An optional lockable cover is

available.

The BC1100 is a DIN rail or chassis plate mounted

controller with LED indication of blowdown status and

potentiometer adjustment of set point and calibration.

A purge button on the front panel manually opens the

blowdown valve.

Features include:-

n 230 V or 115 V (50 - 60 Hz) supply, selectable.

n Switch selectable ranges in ppm or µS/ cm.

n 4 - 20 / 0 - 20 mA output for optional local or remote

display using a DS1000, or can be connected to a

building management system.

n Switch selectable purge time.

The DS1000 digital display unit is an optional extra

that can be used with the BC1100 controller as a local

or remote TDS display. It can also be used as a

remote display unit with the BC3200 or BC3210

controllers.4



The BCV30 and BCV31 are specifically designed for boiler TDS blowdown applications:-

n The valve plug and seat ensure the correct alignment and a tight shut-off.

n To avoid the problems of seat erosion, the valve plug is moved away from the seat before any flow occurs.

n The flow velocities in the valve ensure sludge is not precipitated in the valve.

The blowdown valves

Two types of blowdown valve are available, the electrohydraulically actuated BCV30,

and the pneumatically actuated BCV31, both in DN20 and DN40 sizes.

The DN20 valve has a maximum flow capacity of 1 800 kg/h at a boiler pressure of 32 bar g.

The DN40 has a maximum flow capacity of 11 000 kg/h at a boiler pressure of 32 bar g.

Both valves can be adjusted for different flow conditions.

BCV31BCV30

Pneumaticactuatorspring-to-closeon air/powerfailure

Adjustablegland packing

The BCV30 and BCV31have an adjustable

valve stroke to suitflow conditions.

The valve is suppliedset to 10 mm stroke.The DN20 valve canbe set to 15 mm or

20 mm stroke on siteif required.

The DN40 is fullyadjustable over its

complete range

Air inlet fromsolenoid valve

Cast steel bodywith stainless steel

internals

Manual override

Electrohydraulicactuator

spring-to-closeon power failure

Valve positionindicatorValve position

indicator

Adjustablegland packing

Sample take-offconnection

Sample take-offconnection

5

(DN20 version shown)



Controlling the blowdownSpirax Sarco have developed the BCS4 boiler blowdown system that, by measuring the TDS level in the boiler

water, will minimise the amount of blowdown required, reduce carryover of boiler water and provide automatic

TDS control. The BCS4 system is suitable for shell and water tube boilers. The controllers can be linked to

energy/building management systems.

Calculating the blowdown rate

Before it is possible to select a suitable boiler blowdown TDS control system it is necessary to estimate theamount of boiler water which has to be blown down.

The following information is required:-

1. The required boiler water TDS in parts per million or µS/cm (B).

2. The feedwater TDS in parts per million or µS/cm (F). An average value may be obtained by looking at

water treatment records or a sample of feedwater may be obtained and measured using the Spirax Sarco

MS1.

Note: The feedwater sample must be taken from the feedtank or feedwater line. Do not use a sample of the

make-up feedwater.

3. The quantity of steam which the boiler generates, usually measured in kg / h (S). For selecting ablowdown system, the most important figure is usually the maximum quantity of steam that the

boiler can generate at full-load.

When the information in 1, 2 and 3 is available the required blowdown rate can be calculated as follows:

where:-

F = Feedwater TDS in ppm or µS / m

B = Required boiler water TDS in ppm or µS/cm

S = Steam generation rate kg/ h

SelectionHaving established the required blowdown rate,

check the Table below to ensure that the valve has sufficient capacity at the operating pressure.

Note: Intermediate flowrate strokes can be set on the DN40 BCV30, but not the DN20.

Poor control is causing wastage of boiler water throughexcessive blowdown.

Time

B o i l e r w a t e r T D S

Blowdown rate =B - F

Fx S

The blowdown rate is then given in kg/ h.

Maximum allowable TDS

Average TDS B o i l e r w a t e r T D S

Maximum allowable TDS

Average TDS

Time

TDS controlled accurately, near to maximum level,minimising blowdown, yet avoiding carryover and foaming

caused by high TDS level.

Blowdown valve capacity kg/h

Boiler DN20 BCV30 DN40 BCV30

pressure 10 mm 15 mm 20 mm 5 mm 10 mm 15 mm 20 mm

bar g Stroke Stroke Stroke Stroke Stroke Stroke Stroke

5 380 530 730 450 2 900 3 450 3 550

7 460 710 1 150 475 3 300 4 100 4 500

10 570 950 1 500 500 3 700 4 750 5 450

15 700 1 150 1 650 550 4 550 6 450 7 150

20 780 1 250 1 700 800 5 750 8 100 8 650

32 940 1 400 1 800 1 300 8 400 10 300 11 050

Automatic TDS controlManual blowdown

Manual versus automatic blowdown



Technical information (Dimensions approximate in mm)

12052

112

BC1100 ControllerFunctional range

40 - 400 (ppm or µS/cm)120 - 1 200 (ppm or µS/cm)400 - 4 000 (ppm or µS/cm)

1 200 - 12 000 (ppm or µS/cm)

Supply voltage 230 V, 115 V

Supply frequency 50 - 60 Hz

Maximum ambient temperature 55°C

Protection rating IP40Optional display available (DS1000)

s

48

96 93

DS1000 Digital display unit

Loop powered 4 - 20 mA

Pre-calibrated for percentage indication

Can be scaled to suit controller range (in ppm or µS/cm)

Protection rating IP65 (front panel only)


s

BC3200 Controller

Functional range

10 - 99 (ppm or µS/cm)

100 - 999 (ppm or µS/cm)

1 000 - 9 990 (ppm or µS/cm)




Protection rating IP65

s

161

103193

34Optional cover

72

133144Functional range

110 - 99 (ppm or µS/cm)100 - 999 (ppm or µS/cm)

1 000 - 9 990 (ppm or µS/cm)




Protection rating IP65 (front panel only)

sBC3210 Controller

BCV31 Blowdown valveCarbon steel valve DN20 and DN40, flanged BS 4504 PN40

Also available as BS 10 Table 'H' and BS 1560 Class 300

Maximum pressure 32 bar g

Stainless steel internals

Pneumatic actuator

Air pressure 2 to 6 bar g

Air consumption (20 mm travel) 0.33 litres

BCV30 Blowdown valve

Carbon steel valve DN20 and DN40, flanged BS 4504 PN40

Also available as BS 10 Table 'H' and BS 1560 Class 300

Maximum pressure 32 bar g

Stainless steel internals

Electrohydraulically actuated with manual override

Supply voltage 230 V, 115 V, 24 V


¼" BSPfor sample

take-off

378 (DN20)

426 (DN40)

¼" BSPfor sampletake-off

s

152 (DN20)

200 (DN40)

390 (DN20)

480 (DN40)

152 (DN20)

200 (DN40)

s


http://slidepdf.com/reader/full/control-de-tds 8/8AB I 5SB P403 04

Technical information (Dimensions approximate in mm)

How to order

Controller BC3200 or BC3210 or BC1100Digital display DS1000

Blowdown valve BCV30 or BCV31

(DN20 or DN40)

flanged BS 4504 PN40

Sensor chamber S11 with CP10 sensor and

PT2 plug tail

Stop valve G3, DN20, PN40

Check valve DCV2, DN20, PN40

How to specify

Wall mounted blowdown controller calibrated inµS/ cm and ppm

or

DIN rail / chassis mounted blowdown controller and

loop powered digital display.

Between flange mounting sensor chamber and sensor.

Blowdown valve, DN20 flanged BS 4504 PN40 with

electrohydraulic (pneumatic) actuator with stainless

steel valve internals.

CP10 sensor,S11 sensor chamber, PT2 plug tail

Sensor chamber S11 in stainless steel

DN20 fits between BS 4504 PN16, 25 and 40

BS 1560 Class 300 and BS 10 Table 'H' flanges

G3 stop valveCarbon steel DN20, PN40 stainless steel seat and disc.

Associated equipment

DCV2 check valveStainless steel wafer pattern DN20, PN40

AncillariesSolenoid valve (BCV31 only).

MP2 filter regulator (BCV31 only).

SCS20 sample cooler system.

Strainer for bottom blowdown take-off installations.

MS1 conductivity meter.

Spirax-Sarco Limited, Charlton House,Cheltenham, Gloucestershire, GL53 8ER UK.

Tel: +44 (0)1242 521361 Fax: +44 (0)1242 573342E-mail: [email protected]

Internet: www.SpiraxSarco.com

© Copyright 2004 Spirax Sarco is a registered trademark of Spirax-Sarco Limited

s

Some of the products shown may not be available in certain markets.

PT2CP10

S11

35

107

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