Graduate:Budui Andrei
Guidance Professor:Chief Engineer Gãureanu Adrian
Bucharest 2015
ROMANIAN NAUTICAL COLLEGE
BOILER WATER ANALISYS/TREATMENT
INDEX
1. Introduction;
2. Water treatment applied out of the boiler;
3. Water sampling procedures;
4. Marine boiler water analysis;
5. Marine boiler water treatment
6. Chemical substances used for marine boiler water treatment
1. IntroductionThe concept of employing water, fresh or distilled, as a power
generating source and heat exchange medium originated and was realised with the inception of the steam generator or boiler, and has been applied most successfully and beneficially in this manner ever since. Water has the ability to transfer heat from one surface to another, thereby maintaining the system within the correct operational temperature range while generating steam to carry out work. However, water can adversely affect metal components under the operational conditions normally found in steam boilers and other heat exchange devices. The extent of deterioration depends on the specific characteristics of the water and the system in which it is being used. In order to counteract the detrimental properties normally attributed to water and its contaminants (dissolved and suspended solids and dissolved gases), special chemical treatment programmes have been devised. Accepted water treatment processes and procedures are constantly being upgraded and modernised, and new methods are being developed to complement and/or replace older ones. Unitor utilizes the most modern, practical programmes for the marine operator. Although water from marine evaporators and boiler condensate return systems is essentially “pure”, minute quantities of potentially harmful salts and minerals can be carried by this composition and feedwater into the boiler, where they will accrue, ultimately resulting in serious problems in the steam generating unit. In addition, the water can also contain dissolved gases, i.e. CO2 and Oxygen, which can result in corrosion of the system. Using unprocessed fresh water (e.g. shore water) as a makeup source can present some of the same problems experienced with distilled water, but in addition, certain contaminants which are naturally present in fresh water can be extremely destructive in boiler systems if not dealt with promptly and effectively. Soluble salts such as Chloride, Sulphate and Carbonate are presentas electrolytes in the untreated water, leading to galvanic and other types of corrosion, depending on the conditions in the system.
2. Water treatment applied out of the boiler
Since various substances exist in raw water, the use of the raw water for boilers causes various problems in the boilers and their auxiliary equipments as described. In order to prevent these problems, a proper water treatment should be applied for each boiler system. Boiler water treatments are classified into the chemical treatment (internal) and the mechanical (external) treatment. In ion exchange treatment, dissolved
ions in raw water are removed or exchanged by using ion exchange resins to obtain the appropriate quality of treated water for each boiler system. The removal of all dissolved ions is called the demineralization. The exchange of calcium and magnesium ions with sodium ions is called the softening. The hardness component (Ca2+ and Mg2+) causing scale problems in low pressure boilers are exchanged with sodium ion (Na+) by using cation exchange resins. The ion exchange resins used for the softening are the Na-form of the strongly acidic cation exchange resins. When raw water is passed through the bed containing this resin, the hardness components (Ca2+ and Mg2+) in the raw water are exchanged with Na+ ions of the ion exchange resin and the softened water is obtained as shown in the reactions.
The deaeration of boiler feedwater is carried out to remove the corrosive dissolved gasses (oxygen and carbon dioxide) for preventing corrosion problems in boiler systems. The deaeration utilizes the fundamental principle that the solubility of dissolved gasses in water becomes zero at the boiling point of water. Thus deaeration methods are divided into vacuum and heating deaerations.(a) Heating deaeration In the case of heating deaeration, the dissolved gasses in boiler feedwater are removed by heating the feedwater up to the saturation temperature
(b) Vacuum deaeration Vacuum deaerators remove the dissolved gasses in water by reducing the pressure in the inside to the vapor pressure of the water corresponding to the water temperature. The dissolved oxygen in the deaerated water becomes around 0.1 to 0.3 mg/l. This system is mainly used for low pressure boilers.
Structure of a spray-tray type deaerator
3. Water sampling procedures The sampling is the first step of water analysis. Before sampling,
the purpose of analysis has to be fully understood to obtain the samples which represent the characteristics of aimed plant. For this purpose, the sampling point, sampling time, sampling frequency, etc., are determined by considering the operation conditions of the plant, such as the water flow rate, temperature and the fluctuation of water quality. Since the quality of sample tends to change during the storage, the sample must be carefully stored to maintain its characteristics until the analysis begins.
Analytical items and
methods for water
quality control in
boiler systems
It is the best to perform the water analysis in a well-equipped laboratory. However, simple analysis kits are often used for quick analyses at job sites. The features of those kits are easy analytical methods, easy handling and easy maintenance. The water analysis kit shown is used for boiler and cooling water analysis. The analysis items are alkalinity, total hardness, chloride ion, silica, phosphate ion, sulfate ion, hydrazine, residual chlorine and so on.
Portable pHmeter Portable electric conductivity meter
Water analysis kit for boiler
4. Marine boiler water analysis
Typical water analysis
Daily water quality control is essentially required to keep cooling water systems from corrosion, scaling and biofouling problems. For sufficient water quality control, it is important to understand the influence of each item of water quality on the occurrence of problems, and the relationship between water quality and the effects of chemicals.
Items of water analysis and their meaning
5. Marine boiler water treatment
Troubles in the operation of boiler system and their causes
Example of typical chemical water treatment
for marine boilers
6. Chemical substances used for marine boiler water treatment
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