+ All Categories
Home > Documents > Marine Steam Boiler Water Test Procedures, Impuruties and Treatment

Marine Steam Boiler Water Test Procedures, Impuruties and Treatment

Date post: 16-Oct-2014
Category:
Upload: ian-flack
View: 210 times
Download: 0 times
Share this document with a friend
3
1/13/12 Marine Steam Boiler Water Test Procedures, Impuruties and Treatment 1/3 ZZZ.brighthub.com/engineering/marine/articles/66905.asp[ Written by: Willie Scott • Edited by: Swagatam Updated Sep 1, 2011 • Related Guides: Steam Home > Engineering > Marine Engineering > General Testing of Marine Boiler Feed S\stems Ships boilers are the heart of a steamship, when they are not operating efficiently the ship begins to lose speed. To keep the boilers running at optimum efficiency the testing of marine boiler feed systems before they can cause problems to boiler water pipes and internal fittings is imperative Boiler feed water and condensate systems are regularly tested for impurities, which include gasses and undissolved solids. These combine with water properties such as hardness and alkalinity to deposit scale and cause corrosion of water tubes and internal fittings. Any negative results of the tests can be rectified by the addition of chemicals to the feed water and diluting the impurities by blowing down the boiler and adding make up feed. In the following sections the purpose and equipment used in boiler feed water and condensate testing will be examined. The first section is an overview of the feed system. Overview Superheated steam from the boiler is fed into the steam turbine where it expands through the different stages before exiting into the main condenser. This converts any remaining steam to condensate which is fed through the deaerator, and several heaters before being pumped under high pressure back into to the boiler via the main boiler feed valve. The feed water must be regularly monitored for impurities by taking water samples from the different stages in the feed water system which comprises of the make-up water and condensate returns. Make-up feed being initially supplied by the evaporators, which produce distilled water from seawater. Testing Techniques Samples taken from the boiler water feed system are cooled usually to 25 Ƞ C and tested for the following properties and impurities, Dissolved gasses- Oxygen, Carbon Dioxide and ammonia. Acidit\ or Alkalinit\-Carbonates and bicarbonates Hydroxides content. Hardness – Calcium and magnesium salts content Undissolved solids – impurities built up in the boiler water over time. Chlorine content – usually originates from seawater ingress to feed water system. Methods of Treatment Dissolved gasses of o[\gen, and CO2 It is one of the jobs of the deaerator to remove the dissolved gasses in the returning condensate. So if there are consistently high quantities of dissolved gasses in the system it is best to check that the DA is operating correctly. If however the gasses continue to form, the best method of reducing them is by using a blowdown valve. Some Chief Engineers prefer to leave the boiler on constant blowdown, and I have used this method myself with the provisos, 1. The DA is operating satisfactory 2. The amount of make-up feed is monitored 3. Tests for O2 and CO2 are carried out every watch 4. The steam from the blowdown valve can be used in a feedwater heater. Alkalinit\ Acid and alkalinity are used to describe properties of fluids, their levels being measured in units of pH from 0 to 14, a pH of 7 being neutral. Bright Hub
Transcript
Page 1: Marine Steam Boiler Water Test Procedures, Impuruties and Treatment

1/13/12 Marine Steam Boiler Water Test Procedures, Impuruties and Treatment

1/3www.brighthub.com/engineering/marine/articles/66905.aspx

Written by: Willie Scott • Edited by: Swagatam Updated Sep 1, 2011 • Related Guides: Steam

Home > Engineering > Marine Engineering > General

Testing of Marine Boiler Feed Systems

Ships boilers are the heart of a steamship, when they are not operating efficiently the ship begins to lose

speed.ϝ To keep the boilers running at optimum efficiency the testing of marine boiler feed systems before they

can cause problems to boiler water pipes and internal fittings is imperative

Boiler feed water and condensate systems are regularly tested for impurities, which include gasses and

undissolved solids. These combine with water properties such as hardness and alkalinity to deposit scale and

cause corrosion of water tubes and internal fittings. Any negative results of the tests can be rectified by the

addition of chemicals to the feed water and diluting the impurities by blowing down the boiler and adding make

up feed.

In the following sections the purpose and equipment used in boiler feed water and condensate testing will be

examined. The first section is an overview of the feed system.

Overview

Superheated steam from the boiler is fed into the steam turbine where it expandsthrough the different stages before exiting into the main condenser. This convertsany remaining steam to condensate which is fed through the deaerator, and severalheaters before being pumped under high pressure back into to the boiler via themain boiler feed valve. The feed water must be regularly monitored for impurities bytaking water samples from the different stages in the feed water system whichcomprises of the make-up water and condensate returns.

Make-up feed being initially supplied by the evaporators, which produce distilled

water from seawater.

Testing Techniques

Samples taken from the boiler water feed system are cooled usually to 25οC and tested for the following

properties and impurities,

Dissolved gasses- Oxygen, Carbon Dioxide and ammonia.

Acidity or Alkalinity-Carbonates and bicarbonates Hydroxides content.

Hardness – Calcium and magnesium salts content

Undissolved solids – impurities built up in the boiler water over time.

Chlorine content – usually originates from seawater ingress to feed water system.

Methods of Treatment

Dissolved gasses of oxygen, and CO2

It is one of the jobs of the deaerator to remove the dissolved gasses in the returning condensate. So if there are

consistently high quantities of dissolved gasses in the system it is best to check that the DA is operating

correctly.

If however the gasses continue to form, the best method of reducing them is by using a blowdown valve. Some

Chief Engineers prefer to leave the boiler on constant blowdown, and I have used this method myself with the

provisos,

1. The DA is operating satisfactory

2. The amount of make-up feed is monitored

3. Tests for O2 and CO2 are carried out every watch

4. The steam from the blowdown valve can be used in a feedwater heater.

Alkalinity

Acid and alkalinity are used to describe properties of fluids, their levels being measured in units of pH from 0 to

14, a pH of 7 being neutral.

Bright Hub

Page 2: Marine Steam Boiler Water Test Procedures, Impuruties and Treatment

1/13/12 Marine Steam Boiler Water Test Procedures, Impuruties and Treatment

2/3www.brighthub.com/engineering/marine/articles/66905.aspx

NEXT ARTICLE »

Feed water in ships boilers are best maintained at an alkalinity around 8.5pH, as we go below this figure, the

acidic water will cause corrosion of the watertubes and internals whereas a reading above will cause excessive

coating of scale on these components.

Sodium Phosphate of Soda (NaPo4) can be used to adjust the alkalinity of boiler water.

Hardness

This is caused by high calcium and magnesium content in the feedwater system. Hardness will cause scaling

on the watertubes and internal fittings. It can be controlled by using carbonates, phosphates and certain types

of polymers. Carbonates should be used sparingly as they can promote the formation of CO2 with the

attendant risk of corrosion.

Total Dissolved Solids (TDS)

Dissolved solids build up gradually being left behind in the boiler water as impurities.

Strict control of the TDS is imperative as a build-up can cause carry-over of water from the steam drum. This is

not only detrimental to the turbines but the sensitive auxiliary equipment and instrumentation and should be

avoided at all costs.

Chlorine Content

This falls into the TDS category but it is worthwhile having a closer look is causes and reduction. A rapid rise in

salt PPM indicates a leak of seawater into the feed system, usually from the condenser or process coolers.

Control is achieved again by using the constant blowdown valve and regular topping up of the feed system with

make-up feed water.

Testing Procedures

Testing for Dissolved Oxygen

Indigo Carmine Method

This testing equipment comes in the form of a kit containing all the necessary components to test for dissolved

oxygen content.

A phial is provided containing the correct amount of carmine and measured sample of boiler water is added to

this, which changes the colour of the mixture. This colour is compared to a colour strip and the corresponding

dissolved oxygen content read off.

Testing for Alkalinity

Years ago we used litmus papers of different pH ranges which were dipped into a filtered solution of feed water.

The resultant colour change in the paper, determined whether the sample was acid or alkaline. Not a very

accurate method but gave a quick ball-park indication of the condition of the feedwater. Litmus strips are still

used but give a more accurate result.

Alkalinity tests are also carried out using an electronic instrument, which consists of a glass probe attached to

a meter. The instrument should be calibrated before every test using buffer liquids of known pH.

It operates by immersing the bulbous tip of the glass probe into the feedwater sample, the probe sending a

minute voltage through the solution which is measured and displayed on the meter as pH.

Test for Total Dissolved Solids (TDS)

There are several methods to determine the TDS of boiler feedwater, we shall examine one of the more modern

methods using a TDS meter.

This instrument works on the principle that dissolved minerals and salts affect the conductivity of a liquid such

as boiler feedwater. The instrument measures the waters conductivity and converts the reading to PPM.

References

McKenziecorp: Boiler Blowdown

Cip: Boilers and Steam Raising

Lenntech: Boiler Feed Water

Image Credit

- http://en.wikipedia.org/wiki/File:Scotch_marine_boiler_side_section_(Stokers_Manual_1912).jpg

Page 3: Marine Steam Boiler Water Test Procedures, Impuruties and Treatment

1/13/12 Marine Steam Boiler Water Test Procedures, Impuruties and Treatment

3/3www.brighthub.com/engineering/marine/articles/66905.aspx

Like

WE ALSO RECOMMEND...

What Is The Need To Test Feed Water On Ships?

Marine Boilers - A General Overview

Steam Turbines for Marine Propulsion

Layout of Auxiliary Equipment in a Steamship

Marine Steam Boilers Explained

Add New Comment

Optional: Login below.

Showing 1 comment

Sort by Popular now Subscribe by email Subscribe by RSS

Real-time updating is paused. (Resume)

It is most frequently used by reference to a set of standards against which compliance can be assessed.

Like

blog comments powered by DISQUS

©2012 Bright Hub Inc. All rights reserved.

Post as …

Water Testing Kits 2 months ago

Reply


Recommended