A Steam Boiler is a closed vessel in which water under pressure is transformed into steam by the application of heat. In the boiler furnace, the chemical energy in the fuel is converted into heat, and it is the function of the boiler to transfer this heat to the contained water in the most efficient manner. The boiler should also be designed to generate high quality steam for plant use.
A boiler must be designed to absorb the maximum amount of heat released in the process of combustion. This heat is transferred to the boiler water through radiation, conduction and convection. The relative percentage of each is dependent ulpon the type of boiler, the designed heat transfer surface and the fuels.
Steam Boiler Types
Two principal types of boilers are used for industrial applications:
Fire tube boiIers-Products of combustion pass through the tubes, which are surrounded by water.
Water tube boilers- Products of combustion pass around the tubes containing water. The tubes are interconnected to common channels or headers and eventually to a steam outlet for distribution to the plant system.
The most importand problems in a steam generating system is the Scale and Sludge Deposits, the Corrosion, the Foam and the Carry Over
Common feedwater contaminants that can form boiler deposits include calcium, magnesium, iron, copper, aluminum, silica, and (to a lesser extent) silt and oil.
The most common deposits are :
scale that crystallized directly onto tube surfaces
sludge deposits that precipitated elsewhere and were transported to the metal surface by the flowing water
Corrosion is one of the main causes of reduced reliability in steam generating systems. It is estimated that problems due to boiler system corrosion cost industry billions of dollars per year.
Methods of corrosion control vary depending upon the type of corrosion encountered. The most common causes of corrosion are :
dissolved gases (primarily oxygen and carbon dioxide)
low pH, and
attack of areas weakened by mechanical stress, leading to stress and fatigue cracking
These problems may be controlled through the following procedures:
Maintenance of proper pH and alkalinity levels
Control of oxygen and boiler feedwater contamination
Reduction of mechanical stresses
Operation within design specifications, especially for temperature and pressure
Proper precautions during start-up and shutdown
Effective monitoring and control
From the water side the problems in a steam boiler can be controlled through the following procedures:
External treatment, as the term is applied to water prepared for use as boiler feed water, usually refers to the chemical and mechanical treatment of the water source. The goal is to improve the quality of this source prior to its use as boiler feed water, external to the operating boiler itself. Such external treatment normally includes:
Any or all of these approaches can be used in feed water or boiler water preparation.
Even after the best and most appropriate external treatment of the water source, boiler feed water (including return condensate) still contains impurities that could adversely affect boiler operation. Internal boiler water treatment is then applied to minimize the potential problems and to avoid any catastrophic failure, regardless of external treatment malfunction.
Basically involves the use of chemical additives.
GE Water & Process Technologies range of Boiler Water Treatments includes oxygen scavengers, scale and corrosion inhibitors, condensate line treatments, pH adjusters, antifoams and sludge control agents.
Our range of both traditional and technically advanced products includes the following: Oxygen Scavengers
Tannin Scavenger - is an excellent oxygen scavenger not dependant on the feed-water temperature developed specifically for steam boilers and feed-water systems. It does not add to the boiler water conductivity so reducing the need for blowdown (compared with sulphite)
DEHA - provides outstanding protection from oxygen corrosion and boiler system passivation. It can be used as a replacement for hydrazine in any boiler up to 125 bar without the associated safety hazards and handling precautions. DEHA is volatile and alkaline, contributing no dissolved solids or ammonia to the boiler system
Carbohydrazide - is an organic corrosion inhibitor used for scavenging oxygen and passivating metal surfaces. It can be used as a direct replacement for hydrazine in any boiler without the associated safety hazards and handling precautions. It can be used in boilers of any pressure, up to and including supercritical (220 bar g), and can be fed into feed-waters used for spray attemperation
Catalysed Sodium Sulphite - is an efficient catalysed sodium sulphite product used to absorb oxygen in steam boiler systems. Dose ideally to feed tank to allow time for the oxygen to be absorbed before entering the steam boiler
Multifunctional Sulphite- is an excellent multifunctional product developed for boilers and boiler water systems. Contains catalysed bisulphite, for rapid and complete oxygen scavenging, phosphates for the control of precipitation, and powerful antiscalants and dispersants to mobilise hardness or iron oxide sludges and prevent thereby prevent scale.
Sulphite with Alkalinity Builder
Caustic Based pH Adjuster - concentrated sodium hydroxide based product for use as pH adjuster in boiler water treatment.
Neutralising Amine - cyclohexylamine based neutralising amine condensate line treatment for boilers. Suitable for use up to 2400 psig. FDA approval
Neutralising Amine - morpholine based neutralising amine condensate line treatment for boilers.
Blended Neutralising Amine for Boilers - specially blended mixture contains meutralising amines for boilers condensate line protection.
Combined Phosphate and Polymer Treatment for Steam Boiler Systems - can be used in steam boiler systems up to 1500 psig. and acts as a combined antiscalant and suspended solids control agent. This product is excellent for softened and low hardness water. The phosphate reacts with the hardness whilst the polymer provides transport of calcium, magnesium, iron, phosphate and silica through the boiler, preventing scales adhering to metal surfaces
Scale Dispersant/Sludge Conditioner for Steam Boilers - excellent water treatment products comprising a specially blended mixture of polymeric sludge conditioners developed for use in steam boilers systems
Scale inhibitor/Corrosion Inhibitor for Steam Boilers and LPHW Systems - Blended liquid water treatment product based on polymer sludge, conditioners oxygen scavengers and alkali. Developed for steam boilers and LPHW systems
Sulphamic Acid Descaler and Cleaner with Inhibitor - is a highly active cleaning agent and descaler based on sulphamic acid. The product includes film forming inhibitor to protect mild steel, stainless steel, copper and brass against acid attack.
Hydrochloric Acid Descaler with Film Forming Inhibitor - is a highly active cleaning agent and descaler based on hydrochloric acid includes a special film forming inhibitor to protect carbon steel, copper and brass against acid attack.
Caustic Based pH Adjuster - Concentrated sodium hydroxide based product for use as pH adjuster in boiler water treatment.
Sulphite with Alkalinity Builder
Polymer/Caustic Boiler Treatment - Product for boilers and steam boiler systems. liquid formulation containing an alkali and effective sludge conditioner.
Anti-foam for Steam Boilers - Product for steam boiler applications and prevents boiler water carryover due to foaming.
Polymer Sludge Control - is a polymer based product developed as a steam boiler scale inhibitor and internal metal passivation. FDA regulations.
Combined Phosphate and Polymer Treatment for Steam Boilers - This product is best for softened and low hardness water. The phosphate reacts with the hardness whilst the polymer provides transport of the calcium, magnesium, iron, phosphate and silica, preventing scales adhering to the metal surfaces.
Multifunctional Sulphite for Boilers - contains catalysed bisulphite, for rapid and complete oxygen scavenging, phosphates for the control of precipitation, and powerful antiscalants and dispersants to mobilise hardness or iron oxide sludges and prevent thereby prevent scale.