Boiler and feed water of steam boilers

Few things are more crucial to maintaining a warm and comfortable home than a properly operating boiler system. When you have a dependable boiler, you can always rely on a consistent supply of heat, regardless of the time of year—whether it’s the dead of winter or a chilly evening. However, have you ever given any thought to how these vital heating systems operate on the inside? We’ll dive into the core of boiler operation in this article, paying particular attention to the significance of feed water in steam boilers.

Let’s start by discussing what a boiler truly performs. In its most basic form, a boiler is a closed vessel used to heat water and produce steam, which is then distributed throughout a building to provide heat. It provides warmth to every area of your house like the beating heart of your heating system. But a boiler requires a steady supply of pure, high-grade water in order to operate properly. This is the point at which the feed water is useful.

A steam boiler’s feed water is its vital component. Consider it as fuel for the fire in your boiler. Your boiler just cannot function properly without it. However, why is feed water so important? To begin with, it is used as the raw material for the production of steam. This water is heated by the boiler to create steam, which is subsequently sent to radiators or other heat exchangers via pipes to warm your house.

However, not just any water will do. Feed water must meet strict quality standards to ensure the longevity and efficiency of the boiler system. Impurities in the water, such as minerals and dissolved gases, can lead to corrosion, scale buildup, and other issues that compromise performance and safety. That"s why proper treatment and conditioning of feed water are essential steps in boiler operation.

So how is feed water ready for use in a boiler that produces steam? Usually, it goes through a number of treatment procedures to get rid of contaminants and raise its quality. Based on the particulars of the water source and the boiler system’s needs, this could involve filtration, softening, deaeration, and chemical treatment. Boiler operators can increase efficiency, reduce downtime, and extend the life of their equipment by making sure the feed water satisfies the required standards.

In conclusion, boilers appear to be straightforward appliances, but their internal mechanisms are anything but. In steam boilers, feed water plays a crucial role in both supplying the necessary component for heat generation and guaranteeing the efficient operation of the entire heating system. Homeowners can reap the benefits of consistent warmth and comfort all year long by realizing the significance of feed water and taking the required precautions to preserve water quality.

Boiler Component	Function
Boiler	Generates heat by burning fuel to produce steam.
Feed Water	Supplies water to the boiler to be converted into steam.

In ensuring efficient heating and insulation for your house, understanding the boiler system and the importance of feed water in steam boilers is crucial. The boiler serves as the heart of your heating system, responsible for generating heat through the combustion of fuel. However, its performance heavily relies on the quality of feed water supplied to it. Clean and treated feed water prevents scale buildup, corrosion, and other issues that can hinder boiler efficiency and longevity. By maintaining proper water quality and implementing effective treatment methods, homeowners can optimize their boiler"s performance, reduce energy costs, and prolong its lifespan, ultimately ensuring a cozy and comfortable living environment while minimizing expenses and environmental impact.

Types of water coolant in the heating system

As water moves through the water tube boiler’s water path in the heat supply system, it goes through multiple stages and is given different names as a result.

Water movement in the steam-water path of a water tube boiler at different technological stages:

1. Raw water is raw water from various water sources, which has not undergone mechanical and chemical treatment: municipal water supply, art wells and any open water bodies.
2. Feed water – water entering the water path of the boiler unit. It is pre-treated in the chemical water treatment systems with the quality corresponding to the regime cards.
3. Make-up water – replenishes losses in the heating network caused by water leakage. According to SNIP SP 124.13330.2012 average annual leakage of network water may not exceed 0.25% of the water volume in the main network and consumer networks without DHW pipelines. More specifically, it is calculated for each heating network individually according to the results of adjustment tests.
4. Boiler water – water that circulates through the internal surfaces of the steam boiler. Boiler water temperature in the steam boiler corresponds to saturation pressure, at standard steam capacity.
5. Purge water – water that is purposely released from the internal water circuit of a steam boiler to maintain the standard boiler water alkalinity of ph=9. Continuous blowdown system in the steam boiler is installed according to the results of adjustment tests, blowdown percentage should not exceed 5 % of the boiler steam capacity.
6. Network forward/return – water in the heat network from the circulation pump in the boiler house to the heat consumer and back again.

What is boiler water of steam boiler units

A water-tube boiler uses internal tube heating surfaces to transfer coolant as a source of heat energy. These boilers can be hot water boilers, which generate 95 to 150 degrees Celsius of hot water, or steam boilers, which generate low-pressure steam up to 1 atmosphere, average steam from 1 to 10 atmospheres, high steam from 10 to 20 atmospheres, and ultra-high steam from 20 atmospheres.

Because the steam drawn from the boiler’s drum or steam superheater contains no impurities and is concentrated inside the unit, the operation of a steam boiler is particularly dependent on the quality of the boiler water. This causes the boiler’s salt content to increase multiples depending on the boiler’s steam capacity.

Salts, alkalis, hardness, and impurities are thought to be the most hazardous for it. It is also forbidden to have oxygen or other corrosive gases present.

The most common impurities in source water

Prior to the installation of boilers, particularly medium- and high-pressure steam boilers, the chemical composition of raw water is thoroughly examined, and samples are used to determine the maximum amount of impurities in the feed water.

The boiler equipment factory’s standards for water quality must be met. Create a chemical treatment plan and choose the right equipment to remove dangerous contaminants and chemical elements in the necessary volume from boiler water in order to keep it at the permitted salt content.

Classification of dangerous impurities in raw water that need to be eliminated before the boiler unit receives the feed water:

1. Dissolved substances – solid ingredients: carbonates and sulfates of Ca and Mg. At temperatures above 65 C, they deposit on metal surfaces as scale.
2. Suspended substances, present in the water in the form of suspended solids, mineral or organic base. They are usually not dangerous for the boiler, as they are easily removed by filtering.
3. Aggressive easily soluble gases: O2 and CO2 their presence contributes to corrosion of steel heating surfaces of the boiler.

Hardness

Hard or soft water can be found in raw or source forms. Limescale is a result of the Ca and Mg hardness salts found in hard water. These impurities are either absent from soft water or present in trace amounts. The unit of hardness is µg-eq/kg.

There are two prevalent varieties of hardness:

1. Temporary or alkaline hardness is due to Ca and Mg bicarbonates. These are weak salts that are easily soluble in water and form an alkaline solution. In the process of heating the coolant they decompose, with formation of CO2 and loose sediments, falling out in sludge at high speeds of coolant movement.
2. Constant or non-alkaline hardness is similarly caused by the presence of Ca and Mg salts, but in the formula sulfates and chlorides. As the temperature of water in the boiler increases, solubility decreases and salts turn into hard-to-remove scale. In the presence of silicon oxide, which reacts chemically with Ca and Mg salts, silicates are formed, impairing heat transfer and causing local overheating of the screen tubes with rupture and possible boiler explosion.

The total concentration of Ca and Mg ions in the heat transfer medium determines the overall hardness of the water.

Hydrogen pH

This indicator is crucial to the feed and make-up water treatment system, and it is standardized for each unit separately. The acidic or alkaline reaction in water is represented by the pH scale, which measures the H content of water. It is commonly known that H2O comprises two different types of ions: hydroxyl groups (OH-) and H+ ions.

A solution with a pH between 0 and 6.9 is deemed acidic if H+ is the predominant cation. The solution will have an alkaline characteristic with a pH between 7.1 and 14 when there is more OH- present. When the concentrations of H+ and OH- are the same, water has a neutral property and an index of 7.

Alkalinity

In actuality, boiler water quality is determined by the boiler water’s relative alkalinity, expressed as a percentage. These are the different types of alkalinity in water:

• general (GAL), characterizes the presence of a variety of ions in the coolant;
• hydrate (HCH), NaOH bound to OH- ions;
• Bicarbonate (Bicarbonate Shield), associated with bicarbonate ions;
• carbonate (CK), Na2CO3 associated with carbonate ions.
• phosphate alkalinity, H2PO4 bound to phosphates, when phosphatization of boiler water is applied;
• silicate (CSH), HSiO3 bound to silicate ions.

There is a relationship between these species:

SSHO is equal to SSHF + SSHS + SSHK + SSHG

Alkalinity of boiler water determination. Boiler water in 1 mg-eq/kg is measured in mg/kg.

• 40 for NaOH;
• 84 for NaHCO3;
• 53 for Na2CO3.

Formula for relative alkalinity:

• ЩО – total alkalinity, mg-eq/kg;
• S – dry residue, mg/kg;
• 40 – NaOH equivalent, mg/kg.

It is important to understand that state regulations do not apply to shields for steam boiler units P up to 4.0 MPa that are made by welding and have drums and collectors.

What is feed water

To make up for the steam that the customer removes, this water is supplied to the steam boiler unit via centrifugal or steam pumps. Refueling internal and external condensate losses from consumers in powerful units involves a combination of condensate returned from steam receivers and chemically treated water after the deaerator.

Considering that boiler plants’ chemical water treatment systems differ. Knowing where the feed water begins is crucial. When feed water in boiler plants undergoes deaeration treatment, it first passes through the deaerator before reaching the feed pump suction.

After that, it typically travels to the economizers at the back of the boiler, where it is heated to 155 degrees Celsius, before being fed into the boiler unit’s lower drum and furnace screens.

Normalized feed water quality requirements must be met by steam drum boiler units that use natural water movement and must abide by the following indicators:

• G total hardness P up to 4 MPa not higher than 5/10 µg-eq/l for liquid/solid fuel;
• silicic acid for P from 7 to 10 atm., but not more than 80 µg/kg;
• O2 content, for P up to 10 atm not higher than 20.0 µg/kg;
• pH=9,10.

Boiler water characteristics

Actually, it is feed water that is created when consumers evaporate and remove steam. This procedure causes salts to build up in the boiler, which receives feed water. The salt compartment in steam boiler units with a staged evaporation system has the highest salt concentration.

Iron, temporary hardness salts, and copper are among the contaminants in boiler water that settle out and break down, such as carbonates in the boiler’s water path.

In the boiler unit’s internal circuit, sodium carbonates break down to produce carbon dioxide (CO2) and NaOH, which is removed by steam.

The manufacturer establishes the requirements for boiler water quality, which are then kept an eye on by the operating staff through boiler water sampling.

What the quality of boiler water affects

It is necessary for the boiler unit and its associated equipment, such as electric pumps, turbines, and heat recovery units, to operate. Scale formation is the most hazardous process brought on by low-quality water.

Scale buildup considerably lowers boiler efficiency and accumulates inside the convective tubes and screen. This results in overheating zones and poor heat transfer from the flue gases to the boiler water.

Overburning of pipes will eventually cause them to burst, releasing hot water into the furnace area at high pressure inside the boiler.

When boiler water is released suddenly, the pressure inside the boiler drum drops. The superheated water instantly turns into steam, which has a volume multiple of the water volume. This creates a shock force that can rupture the boiler unit’s structure and launch the drum hundreds or even thousands of meters away, demolishing the boiler room buildings.

The existence of oxygen in boiler water, which influences the initiation of corrosion processes on steel boiler tubes, collectors, and drums, is equally hazardous. A large portion of the boiler’s surfaces are susceptible to corrosion when the water’s pH is below 7.

Alkaline water has a pH of over 9.5, which causes it to foam violently, distort the actual water level in the boiler drum, and trap the foam with steam, which is extremely dangerous for equipment that uses steam. Moreover, higher alkalinity fosters intergranular fracture and makes steel components more brittle.

Requirements and quality standards for water in the steam and water path of the boiler

State standards and the manufacturer’s mode maps used in the design and production of each boiler are used to normalize the water quality in the boiler unit.

Additionally, the project of chemically treating water to remove aggressive gases and dangerous substances is being developed. Following the boiler and chemical water treatment plant equipment installation, adjustment tests are conducted to determine the unit’s water-chemical regime and the technology for both continuous and intermittent blowing.

The primary markers of the chemical makeup of boiler water in drum boiler units featuring tube rolling and welded drums with P values up to 4 MPa are:

1. Relative alkalinity up to 50%.
2. Jo= 5/10 for liquid/solid fuel, µg-eq/kg.
3. Transparency determined by the Font method – 40 cm.
4. Fe= 50/100 for liquid/solid fuel, mg/kg
5. Cu= 10/not standardized for liquid/solid fuel, µg/kg.
6. Dissolved O2 content = 20/30 for liquid/solid fuel, µg/kg
7. pH value = 9.0 at 25 C.
8. Content of oil products- 0.5 mg/kg.

Methods of boiler water quality control

All types of water-tube boiler units must control the qualitative composition of the boiler, feed, blowdown, and make-up water in compliance with RD 24.032.01-91 guidelines.

The chemical water treatment project and the adjustment test data establish the chemical control volume. It is required to ensure the long-term and effective functioning of the boiler room’s primary and secondary equipment, including the boiler’s steam and water path.

Chemical control provides a quantitative understanding of the quality of raw water and variations in its composition in the condensate pipeline, chemical water treatment system, and boiler steam-water path. These data are used to calculate the boiler unit blowdown size, steam humidity, condensate return percentage, and deaeration unit operation efficiency.

Understanding the function of boilers and feed water in steam boilers is essential to maintaining the longevity and efficiency of your home heating system. The central component of steam heating systems, boilers provide the heat your house needs to stay warm in the winter. The performance and longevity of boilers, however, are greatly influenced by the quality of the feed water that is provided.

Feed water contaminants, like dissolved minerals and gases, can lead to corrosion, scale accumulation, and other problems in the boiler system. This can result in expensive repairs and early component failure in addition to decreasing efficiency. Therefore, in order to avoid these issues and guarantee boiler operation at its best, feed water treatment must be done properly.

Filtration, softening, and chemical treatment are a few examples of water treatment techniques that help keep feed water pure and free of contaminants. While softening lowers the concentration of hardness minerals like calcium and magnesium, filtering eliminates solid particles. To stop corrosion and scale formation, chemical treatment involves adding inhibitors or neutralizing agents.

For problems with the boiler and feed water systems to be found and fixed quickly, regular maintenance and monitoring are also essential. This include looking for leaks, monitoring the chemistry of the water, and cleaning or replacing any worn-out parts. Homeowners can extend the life of their heating systems and prevent expensive malfunctions by taking preventative measures.

In conclusion, homeowners hoping to maintain dependable and efficient home heating must comprehend the significance of boilers and feed water in steam heating systems. People can make sure their boilers work as efficiently as possible and keep their homes warm and cozy for many years to come by investing in appropriate water treatment and routine maintenance.

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