How does water quality affect the efficiency and lifetime of the power plant equipment?

The presence of hardness salts in water leads to pipewall scaling, which in its turn leads to a decrease in heat transfer and installation efficiency. Oxygen in boiler water causes intensive corrosion of the equipment and pipe walls. It increases capital costs due to shutdowns and repairs and, as a result, lresults in profit losses of the enterprise.

What are the main contaminants to be removed from water before its use at a power plant?

Some of the “harmful” components are Ca2+, Mg, CO32-, SO42 ions, dissolved oxygen and CO.

What role does filtration play in the water treatment process for power plants?

Filtration allows for additional purification of water from small impurities that could not be removed at the previous stages of clarification, settling and lime softening. Small particles can “poison” the load material (ion-exchange resins) or destruct membranes in reverse osmosis systems.

How often should water quality testing and monitoring be conducted at a power plant and what parameters are usually measured?

The fed water analysis is regularly carried out in laboratories of the power plant once a day for checking the following parameters: pH, temperature, color, turbidity, hardness salt content, the presence of carbonic acid, sulfuric acid ions, suspended substances, nitrates, chemical oxygen demand and biochemical demand.

Water Treatment in the Steel Industry

Intro

Today electrical energy is generated in industrial countries at steam-power plants with the use of fossil fuels: coal, natural gas, fuel oil and enriched uranium. Thus, in 2022 70.1% of the total amount of the world’s electricity was generated at such power plants. It requires large amounts of water.

Water treatment for a steam-power plant is a very important task, since the reliability and cost-effectiveness of equipment operation depends on the water quality. To ensure longtime operation of a steam turbine unit without deposits in water tubes, superheater and turbine whealspace the individual components concentration in feed water should not exceed 5 – 100 μg/kg.

And only advanced treatment methods make it possible to obtain such water in required large quantities throughout the entire period of the power plant operation.

Power Plant Water Treatment Systems and Solutions

At power plants water is used for:

Filling the steam-turbine plant circuit and compensation of steam and condensate losses.
Heat networks make-up.
Heat extraction in turbine condensers and auxiliary heat exchangers.

The main tasks that M HEAVY TECHNOLOGY experts solve water treatment projects at power plants are:

✔️ Increasing reliability and extending the service life of power equipment of the enterprise;

✔️ Reducing capital costs for equipment operation;

✔️ Reducing harmful wastewater emissions.

In each technological process feed water is subjected to appropriate treatment. The choice of purification method depends on the source of water supply and is determined by the requirements to the final water analysis, power plant parameters and used equipment.

Power Plant Water Treatment Technologies

There is a huge number of power plant water treatment technologies. However, basically they can be divided into reagent-free and chemical methods.

Reagent-free or physical methods are used as separate stages in the general technological water treatment process and as independent methods to obtain water of the required quality.

Chemical methods are those using various chemical reagents.

When designing a water treatment system for thermal power plants M HEAVY TECHNOLOGY uses an integrated approach, which includes both physical methods by means of membrane filters and water purification with addition of chemical reagents.

Pre-treatment

The stage of water pre-treatment is necessary to simplify and improve water parameters at subsequent treatment stages. It is mainly carried out with the help of sand or high-speed pressure filters. At this stage insoluble particles are removed.

Lime-soda water softening

✔️ coagulation and precipitation of colloidal impurities;

✔️ lime treatment, desilication and lime-soda precipitation (softening);

✔️ filtration.

As a result of these water treatment methods solid waste (lime and gypsum) is formed, which does not require special disposal, but is used for production of building materials.

Water treatment using ion exchange method

Water does not practically contain coarse and colloidal impurities after preliminary purification, but a large amount of dissolved substances still remains and should be removed.

Water treatment by means of the ion exchange method includes:

✔️ reverse osmosis and ultrafiltration;

✔️ electrodialysis;

✔️ desorption of gases from water.

As a result of using these water treatment methods wastewater with a high content of sodium chloride is formed, therefore thermal desalination is used for disposal of such water.

Cooling water stabilization

To improve water quality and boiler equipment performance chemical reagents are added into the water. Thus, scale formation and corrosion are excluded.

Thermal water desalination

For wastewater disposal they use evaporators. As a result of their work steam for technological processes, distillate and salt are generated.

Power Plant Water Treatment Process

Depending on the source of water supply different approaches to the water treatment are used. The most common water supply source is surface water (river, lake, impoundment), which is characterized by high degree of coloration, turbidity and presence of microorganisms, especially in flood periods.

Boiler feedwater

The highest demands are placed on water, used for filling the circuit of a steam turbine plant and its make-up during operation.

To fill the circuit of the steam turbine plant and make-up of internal losses only highly demineralized water is used. Such water is obtained by chemical and thermal desalting methods. Heating networks are filled with water softened by ionization.

With the use of chemical treatment, including ion exchange methods, it is possible to obtain both softened and highly demineralized water. By one of the most common physical methods at thermal power plants – thermal treatment of water – they always obtain a distillate, i.e. water with a very small content of impurities. However, softened water, which has already undergone chemical treatment or ionization is also used in a number of cases while heat treatment, carried out for high desalination.

To ensure the required quality source surface water is primary clarified in horizontal settling tanks by means of coagulants and flocculants. Then the water is filtered in self-cleaning filters and goes through a softening stage. It means a lime-soda water softening with application of subsequent ultrafiltration and reverse osmosis.

The choice of technology depends on the type of boiler equipment used and feedwater requirements. Having passed the stage of removing hardness salts the water is supplied to a unit for removing dissolved О₂ and СО₂to reduce corrosion. After all stages of cleaning anti-corrosion inhibitors are added to the water before it comes into a boiler.

Equipment cooling

Recycling water, used for equipment cooling, requires less purification and treatment. It goes through similar stages, with the exception of high desalination and degassing, since the temperature regime of closed circulation systems is lower than that of the water used for steam production, and corrosion intensity or deposition of hardness salts content are lower.

Heating networks make-up

To compensate losses, caused by evaporation and droplet entrainment, the circulating water supply system is made-up with fresh water, which antiscalants and biocide are additionally added to, in order to reduce the intensity of hardness salts sedimentation on the equipment walls and pipes, as well as to prevent the growth of microorganisms.

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Our Experience in Water Treatment for Power Plants

A bright illustartion, demonstarting an individual approach and use of integrated solutions in water treatment technologies of M HEAVY TECHNOLOGY, is designing a water treatment department for the oxygen-converter plant (BOF shop) of METINVEST SICHSTAL. This complex of works includes preparation of water of different quality for various consumers of the plant, including preparation of high quality water for waste heat boilers of the converter department.

Description of water treatment technology:

The developed scheme consists of two blocks, including:

a membrane-type cleaning method;
mechanical treatment.

Feed water is taken from the Dnipro river.

The feed water quality and the final result are represented in table 1

Parameters, UOM	Feed water from the Dnipro river	Required demi-water quality “DW”	Water quality after all filtration stages
Temperature, ^oС	15 – 35	30	15-35
pH value	7 – 8,1	9 – 10	6,3 – 8,5
Total hardness, mmol/l	< 3	< 0,01	< 0,00002
Calcium hardness, mmol/l	< 2,5	–	< 0,00001
Alcalinity, mmol/l	< 1,6	–	< 0,0002 < 0,0006*
Electric conductivity, µS/cm	< 800	< 2	< 0,06 (0,015*)
Fe content, mg/l	< 0,5	< 0,03	no
Chlorides Cl, mg/l	< 70	–	< 0,0015
Mn content, mg/l	0,052	–	no
Sulphates SO₄, mg/l	< 60	–	< 0,0002
Silicates SiO₂, mg/l	< 20	< 0,02	< 0,0005
O₂content, mg/l	< 0,02	< 0,02	< 0,02
Corrosivity СO₂, mg/l	no	no	no
Oil content, mg/l	< 5	< 0,5	no
Bacterial count at 20^oС for 48h, Bacteria, ml	< 104	–	no

* depending of the reagent type chosen.

From the reservoir it is pumped to a mechanical filtration unit, which includes 6 parallel filters.

The resulting clarified water comes into a reservoir and then is fed to consumers by means of two groups of pumps.

The other part of the flow is fed to an ultrafiltration unit by pumps after being cleaned in 4 mesh filters.

Ultrafiltration is represented by 4 parallel installations. Subblocks operate in a cascade mode.

The resulting permeate water from the ultrafiltration units is fed by 4 pumps through a reservoir to the reverse osmosis of the first stage of purification. The filtrate flow is first filtered through 5 micron cartridge filters. At the same time bisulfite and antiscalant are added to the stream by means of metering stations.

Reverse osmosis installation No. 1 is represented by 4 parallel subblocks. To carry out the membrane separation process a working pressure of 5-8 bar is created in front of the membrane blocks using frequency-controlled pumps (1 pump for each subunit).

Permeate of appropriate quality from reverse osmosis No. 1 is going to consumers.

Then the required part of the permeate is supplied through a reservoir to reverse osmosis No. 2 of the 2nd filtration stage.

The permeate stream is pre-filtered through 2 parallel 5 micron cartridge filters. At the same time, NaOH is added into the permeate stream.

Reverse osmosis installation No. 2 is represented by 3 parallel subblocks. To carry out a membrane-type separation process a working pressure of 8 – 11.5 bar is created in front of the membrane blocks by means of frequency-controlled pumps.

After that permeate from reverse osmosis No. 2 comes to an electro-deionisation unit.

The electro-deionisation unit is represented by 2 parallel blocks. The concentrate is discharged into a desalinated water reservoir. Ultrapure water of the required “DW” quality class is discharged into a desalinated water reservoir, where from it is fed for needs of the waste heat boiler of the converter section with the help of 3 frequency-controlled pumps.

All filter units in the system are equipped with electromagnetic flowmeters for monitoring performance and with pressure sensors for monitoring pressure drop.

The scheme also includes a wastewater treatment system for each filter unit.

M HEAVY TECHNOLOGY experts pay special attention to compliance with environmental standards and develop highly efficient wastewater treatment systems.

How M HEAVY TECHNOLOGY Can Help with Power Plant Water Treatment

The work of M HEAVY TECHNOLOGY specialists in designing water treatment systems for power generation industry is aimed at:

☑️ Increasing lifetime of the equipment.

☑️ Increasing energy production efficiency.

☑️ Increasing operation reliability and safety of the power plant.

☑️ Compliance with environmental standards for operation of energy generating enterprises.

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