Any water heating equipment, whether it is a domestic or industrial boiler requires a certain quality of water. Most restrictions are due to the fact that at higher temperatures, scale is formed, which leads to the unfortunate consequences. Below we will talk in detail about what are the consequences for the boilers water, to what indicators to purify water, and what types of water purification equipment are suitable for water treatment for steam and water boilers, and heat exchangers.
Boiler water requirements
The quality of water for industrial boilers is determined by the equipment manual or a normative document. In Ukraine this is GNAOT 0.00-1.08-94 “Rules for arrangement and safe operation of steam and hot-water boilers.
What do the various impurities lead to, we explain below.
Colloidal and mechanical impurities
Large mechanical particles are represented mainly by sand and clay, sometimes also by rust and scale particles. The composition of these visible particles that cause increased water turbidity depends predominantly on the water source (well or pipeline). Also corrosion products from metal pipes and heating elements can enter the system. In the case of exceeding the allowable values of such components are often observed breakdowns of pumping equipment, shut-off and control valves, clogging of pipes and, consequently, reduction of their cross section.
As for soluble impurities, it will be rational to divide them into several groups, which we will do below.
Calcium and magnesium carbonates are the base components of limescale. At elevated temperatures they tend to precipitate faster, forming a uniform lime crust. It is also worth noting that components such as calcium sulfate, silicates, manganese and copper compounds also have the ability to crystallize at temperatures above 100o C. The sulfates, for example, have a crystallisation point of 130 °C.
Formed plaque disrupts the heat dissipation process of surfaces and leads to a decrease in boiler output. This, in turn, leads to an increase in energy costs and reduces the service life of boilers. The formation of even a thin layer of scale interferes with the heat exchange and can lead to metal overheating and subsequent cracks and fractures in the pipe surface.
There are also a number of impurities that can accompany corrosion processes. It is important to know that there are two types of corrosion: chemical and electrochemical.
Chemical – refers to the process of destruction of the material under the influence of aggressive components of water, but the electrochemical is based on the fact that on the metal surfaces are created micro-galvanic pairs primarily with iron and manganese ions.
Dissolved gases O2 and CO2 – are impurities, which are the main generators of corrosive processes in boilers due to oxidative properties. Also one of the important parameters in reducing corrosivity is the pH of the water. You need to correlate it according to the chemical properties of the pipe metal. For example, aluminum is stable at a pH of 8.3 to 8.5, but iron can be unstable to corrosion if the pH < 9.
Chloride corrosion leads to the destruction of the passivating film, so the chloride content in water is regulated by the value of 150-200 mg / l.
These are substances that lead to the formation of foam, mainly phosphates, alkalis, lubricating oils and petroleum products. It is worth noting that these components are partially added to the water in order to neutralize hardness salts and prevent scaling. These impurities are especially dangerous for steam boilers, because they lead to contamination of steam and formation of sludge of impurities entrained in foam on the turbine blades.
It is important to know that the higher the heating temperature, the cleaner must be the water, which is fed to the boiler. Also more stringent requirements are set for closed-loop systems.
Boiler water treatment
Here we explain how to prepare quality water for boilers with modern technology and how to improve outdated systems.
To begin with there are two basic technologies: ion exchange and reverse osmosis.
Depending on the type and nameplate requirements of the boiler equipment, one of the system types is selected. The quality of the source water already requires additional pre-treatment steps and the addition of certain reagents during the treatment process.
Also the technological scheme is partially justified by the capacity or output of the boiler. We will not give a classification of boilers, because this material is still devoted to water treatment, but not boiler equipment.
Domestic water treatment for boilers
Small domestic or commercial hot water boilers come in gas, electric and solid fuel. Their capacity is often up to 30, less frequently up to 50 kW. The water quality of such systems is usually not regulated in the manual. But the turbidity and hardness of the water still ultimately leads to increased heat loss, as well as the need for regular maintenance. In terms of water treatment, these can include domestic boilers.
For boiler water treatment at home we recommend the installation of softening systems or integrated treatment for the whole house. Such installations have small dimensions and often consist of such elements:
- mechanical cartridge or mesh filter to remove sand, rust and silt;
- complex treatment system with Ecomix material for hardness, iron content and water color reduction or water softening system with ion-exchange resins;
- optional charcoal filters and UV lamps can be installed.
Read more about how filtration systems work for your home in our article about domestic water treatment.
A simpler, more compact and cheaper solution is the installation of a boiler scale filter. These devices are installed directly in the pipeline in front of the boiler or boiler and are a bulb, inside which there is a replaceable cartridge containing pellets or crystals. They are able to release a small amount of substance into the water passing through them, which binds hardness salts, preventing the formation of scaling on the heating elements and piping of water heaters. The disadvantage of such a system is the narrow efficiency of the filter – virtually zero efficiency in relation to iron, organic impurities, etc.
Flushing of the domestic boiler
The second step is to flush the boiler, which is one of the maintenance steps. It can be carried out by yourself or with the help of specialists. Flushing must be performed according to the instructions or as soon as the following signs appear. For example, the constant switching on the burner, the constant hum of the circulating pump, the long heating of the radiators in the house, the increase in gas consumption for normal use, the decrease in the pressure of hot water.
Two methods are used for flushing: demountable and non-dismountable. The names generally describe the cleaning principle. The disassembly process disconnects the boiler from the water and power supply, and soaks all the parts in the solution for 10-12 hours. The dry method involves disconnecting from the coolant, the heating system and connecting to a special device that circulates a solution of reagents for 6-8 hours.
Acidic reagents are used to flush boilers, which can dissolve scale deposits without affecting the surface of the heat exchanger tubes.
Commercial and industrial boilers
Above we told about domestic boilers, now let’s talk about water treatment for large hot water and steam boilers. In this case, the water quality is a very serious parameter. It is strictly regulated by regulations and depending on the type of boiler will play a major role in the operation of equipment.
Water boilers are used mainly for heating and hot water supply of residential and non-residential buildings, also sometimes as supplementary equipment for thermal power plants and for production purposes. The nominal water temperature at the boiler outlet, which can range from 70 to 115 °C, determines the water quality, as the intensity of scale formation is directly proportional to temperature.
When heating water up to 100 o C, the standard water hardness will depend on the boiler capacity, but if the boiler produces overheated water, then there are strict requirements for other components.
As for steam boilers, the requirements to the boiler water are much more stringent, since there is essentially heating of the water to a vapor (ie first boiling, followed by superheated steam), respectively, the processes of sludge formation are more intense. The degree of water purity depends on the operating pressure. The most stringent requirements are imposed on water for critical (18-20 MPa) and supercritical (over 22.5 MPa) pressure boilers, operating at thermal power plants.
Below we give the standard values for water quality for steam boilers and waste heat recovery boilers.
Boiler water treatment schemes
The traditional water treatment system involves several stages.
- Mechanical purification to reduce water turbidity (1) – this step is mandatory in any water treatment scheme. The traditional use of backfill filters with quartz sand.
- De-ironing/Demanganization to remove iron and manganese impurities, which oxidize quickly at elevated temperatures, forming sediments and suspended solids, and also contribute to corrosion, or the purification of water from organics on charcoal filters. These filters are designated by position (2). It is worth noting that this stage is excluded if the water quality is initially good.
- Two-stage water softening with ion exchange resins (3.5) – hardness salt cations (calcium and magnesium) are replaced with safe, non-scaling sodium cations in the ion exchange process. When the material is exhausted, it is regenerated with a sodium chloride solution from the solvent tank (4.6).
- Dosing of chemicals (7): pH controllers, antiscalants, etc.
This scheme provides water quality that can fully meet the needs of hot water boilers, as for steam boilers, the use of such water for steam boilers of critical and supercritical pressure leads to increased energy costs and frequent flushing of heat exchangers.
Another disadvantage of this technology is a large number of units of rather oversized equipment and, accordingly, the area that it occupies.
What modern water treatment can offer?
There are two basic schemes: the same two-stage ion exchange with certain improvements or reverse osmosis. Both technologies are used for water boilers and steam boilers.
José Padilla Boiler Room Bali DJ Set
Ion Exchange Technologies
The company hydrogen.best-store-us.com has implemented many projects with advanced circuitry. It is worth noting that during the implementation of such projects for old boilers, equipment that was installed earlier is usually partially used. Here is a scheme that we offer to our customers.
In the first stage (1) mechanical filters are installed. Depending on the quality of source water, it can be either disc or backfill filters. The benefits of disc filters:
- it is not necessary to wash and refill the filtering material, such filters are washed manually or automatically with a relatively small volume of source water;
- compact size of disc filters allow to use the production area more efficiently.
In the second stage, depending on the type of water, two types of systems can be installed (2):
- Softening system (Na-cationic exchange) for removal of hardness salts from water, this installation is suitable if the water is of high quality, does not have high colouring and does not contain iron and manganese;
- The Ecomix complex water treatment system ensures iron and manganese removal as well as softening and color reduction.
Regeneration in both cases takes place with a sodium chloride solution from a salt tank (3).
The equipment is installed in such a way that when one filter enters the regeneration mode, the others can work. This ensures a continuous water treatment process.
The next step is the installation of a secondary water softener (4). It is always Na-cationic. Regeneration is performed from a tank of saline solution (5). The plant also works in continuous operation.
In the final stage, reagent solutions are dosed into the water (6,7):
- pH regulator – usually these are alkaline reagents, which increase the pH value of water to the required level;
- anti-scalants – substances that prevent the formation of scaling crystals;
- Oxygen binders;
It is worth noting that if the quality of the source water is high, softening can take place in one stage.
It’s probably the best solution for treating water for steam boilers. Depending on the number of reverse osmosis stages, it can provide virtually demineralized water that will provide maximum energy efficiency for the system. According to research and the experience of our customers, expensive reverse osmosis systems pay for themselves within about a year.
Folamour | Boiler Room: Streaming from Isolation
Electrodeionization systems are also used in thermal power plants.
Below is a diagram for a small steam boiler.
In the first stage, mechanical filters (1) are installed, which can be disc, strainer or backfill filters that meet the conditions of preliminary mechanical purification.
The next step (2) will be the removal of specific impurities to bring the water to a state that is safe for reverse osmosis membranes.
If the system works on tap water, it can be charcoal filters to reduce chlorine and organic substances. If the system works on well water, it is possible to install deferrizers.
If the water quality is sufficient for the safe operation of reverse osmosis membranes, the first and second stages can be omitted.
The reverse osmosis system consists of cartridge pre-filters to remove particles larger than 5 microns, controlling devices and a unit of membrane elements, which, in fact, is the heart of the system. Reverse osmosis traps 99% of water impurities, minimizing the need for boiler blowdowns.
After deep cleaning, water flows to a storage tank (5) and from there to the boiler. The necessary reagent solutions are then introduced into the pipelines from the dosing systems (6).
Closed loop filter
Modern boiler equipment also includes mechanical filters for closed circuits. They are able to remove particles of rust, limescale greater than 25 (50*) microns and magnetic particles (oxides of metals, etc) from boilers.).
* Depending on the model of.
The device consists of:
- Stainless steel housing and cover;
- Depending on the bag filter model;
- magnetic element;
- an adjustable pedestal.
hydrogen.best-store-us.com has extensive experience in implementing solutions for boilers ranging from small boilers for the food industry to large systems for thermal power plants.
Preparation of water for thermal power plants, which operate at high and ultra-high pressures, requires even deeper purification. In the case of Kiev CHP 6, a system was developed that consisted of two stages of reverse osmosis and electrodeionization.
We have tried to talk as concisely as possible about what problems should be solved filters for the boiler, and what modern water treatment offers. If you have any other questions regarding the material in this article, we would be happy to answer in the comments.