Boiler Water Treatment

1. Background.

To achieve carbon peaking and carbon neutrality at home and abroad, how to achieve green development through energy conservation and emission reduction is an important issue facing the development of enterprises. The boiler is one of the main equipment for energy conversion in the production process of enterprises, but there is generally about 5% energy loss when boilers blow down. One of the key factors affecting the heat loss of boiler blowdown is the water quality of the water supply system during boiler operation.

Figure1 Boiler water.

Therefore, suitable boiler water treatment technology should be found to improve the water quality of the boiler, thus improving boiler operation efficiency, reducing the sewage discharge of gas-steam boiler and achieving the purpose of saving energy and reducing consumption. However, NEWater Company uses reverse osmosis technology to treat boiler water quality in boiler water supply system, which can not only solve the chloride ion pollution problem existing in traditional sodium ion exchange resin method, but also obviously reduce the boiler sewage, effectively improving the utilization rate of resources, and achieve the purposes of energy saving, consumption reduction, and environmental protection.

2. Purpose of Boiler Water Treatment.

The treatment result of feed water of boiler make-up water is one of the important factors affecting the stable operation of the boiler. Unqualified feedwater treatment will cause scaling and corrosion of the boiler. Because of the scaling phenomenon caused by poor water quality, it is easy to cause burning loss, bulging, cracking, and other phenomena on the heating surface of the boiler. The above factors will reduce the boiler steam quality, resulting in a large amount of boiler sewage, resulting in high energy consumption of boiler operation.

It deviates from the current development trend of energy-saving and environmental protection, so reliable measures must be taken to effectively treat the water quality of the boiler in the process of boiler operation. Effective methods are adopted to remove ionic impurities harmful to boilers in water, to ensure the control of water quality, avoid the damage of unqualified water quality to boiler operating components, ensure steam quality, ensure boiler operating efficiency and reduce the generation and discharge of sewage during operation.

The following will introduce how the reverse osmosis water treatment system developed by NEWater is applied to reverse osmosis treatment of feed water of offshore thermal recovery boiler and reverse osmosis treatment of utility boiler water.

3. Application of Reverse Osmosis Water Treatment in Boiler.

3.1 Reverse Osmosis Treatment of Feed Water for Offshore Thermal Recovery Boiler.

The recoverable reserves and production of conventional offshore oilfields are decreasing year by year, but their super-heavy oil reserves are huge and have not been used. To make up for the decline of crude oil production, thermal recovery of super heavy oil has become the main measure and development direction of offshore oil and gas field development.

The steam injection system is the core of thermal recovery, which mainly includes a boiler water treatment system and steam injection boiler. The inlet water quality standard of steam injection boilers is extremely high, which requires no oil, zero hardness, and low salinity make-up water. Unqualified inlet water quality will cause boiler scaling and coil corrosion, increase maintenance work, and even cause safety accidents.

Figure2 Boiler feed water for offshore heavy oil thermal recovery.

Therefore, a reliable boiler water treatment system plays a vital role in thermal recovery and is the key to the safe, continuous, and stable operation of the steam injection system.

The boiler feedwater treatment system developed by NEWater Company can be used to remove impurities in water such as suspended solids, salt, and dissolved oxygen, and meet the water quality index of boiler population, to discharge heat loss, save energy and reduce emissions. The system includes a pretreatment unit and a desalination unit.

Figure3 Reverse osmosis treatment equipment for feed water of offshore thermal recovery boiler.

• Pretreatment Unit

The pretreatment unit mainly removes suspended solids such as solid particles and colloids and adjusts the temperature of raw water. The pore size of the reverse osmosis membrane is extremely small, and there are many suspended solids in the influent, which will cause fouling of reverse osmosis membrane, resulting in decreased membrane flux, increased cleaning frequency, and difficult operation and maintenance. Therefore, a stable and efficient pretreatment unit is the basis for the normal operation of the boiler feedwater treatment system, and it is generally necessary to reduce the turbidity of raw water to below 1NTU.

Ultrafiltration membrane is a selective permeation membrane that separates solvents and solutes according to particle size. It can separate particles of ten nanometers by pressure drive, remove bacterial colloids and macromolecules in water, and reduce the turbidity of raw water to 1. The main difference between organic ultrafiltration and inorganic ultrafiltration lies in the different membrane materials and operation modes. Inorganic ceramic membrane ultrafiltration is more wear-resistant, usually adopts large-flow cross-flow filtration, and can tolerate higher suspended solids; For organic ultrafiltration, it is generally necessary to reduce the turbidity of influent to below 5 to ensure long-term stable operation.

Multi-media filter is conventional equipment for offshore oilfield water treatment, which uses filter materials with different particle sizes and materials to adsorb, coagulate and filter suspended matter in water step by step. The turbidity of inlet water is less than 20, and the turbidity of outlet water can reach 5.

• Desalination Unit

The desalting unit removes salt from raw water such as NaCl, CaCl, MgCl, etc., to avoid the risks of scaling, burning through, and corrosion of boilers. The desalting process is quite different with different boiler water treatment indexes. This study studies desalting schemes with different depths based on the reverse osmosis membrane method.

The reverse osmosis process refers to the reverse osmosis process in which brine is separated by applying an external driving force to overcome osmotic pressure and making water molecules pass through the reverse osmosis membrane. Reverse osmosis membrane is a selective permeation membrane that can separate sub-nanometer (low molecular salt) particles according to their size. Desalination gradient design based on the concentration of soluble solids in seawater, the first-stage reverse osmosis can desalinate more than 97% and the water recovery rate can reach 40% within three years; The secondary reverse osmosis treatment can desalinate more than 98%, and the water recovery rate can reach 85%. Different desalination units are adopted according to different boiler water quality.

Figure4 Reverse osmosis treatment flow of feed water of offshore thermal recovery boiler.

The water quality index does not require high salt content, so primary reverse osmosis and ion exchanger can be used to meet the requirements. The active Na2+ in the resin for the ion exchanger can contact the plasma of Ca2+and Mg2+in the exchange water. The purpose of softening raw water can be achieved, and the comprehensive water production rate can reach 35%. At the same time, it reduces the sewage discharge of the boiler, saves energy, and reduces consumption.

3.2 Reverse Osmosis Treatment of Boiler Water in Utility.

In recent years, the rapid development of industry at home and abroad has increased the electricity demand. In addition to the application and development of renewable energy such as wind energy and solar energy, coal and other resources are the main energy for electric energy development, and more power plants have been built. Coal resources have large energy and can meet the electricity demand in most areas, so coal resources are the main resources for electric energy development.

Figure5 Utility boiler water.

However, this development mode needs boiler combustion, which requires high water quality of boiler. How to treat boiler water of utility has become a key research problem, and NEWater Company has solved this difficulty well.

Reverse osmosis technology is a comprehensive technology for efficient treatment of raw water using filters, water tanks, pumps, and other devices, which is mostly used for water quality improvement. NEWater selected this technology as the core technology of boiler water quality treatment. Using reverse osmosis treatment technology, a set of boiler water quality reverse osmosis treatment systems is constructed by concentrating multiple appliances, to eliminate impurities in the boiler water. After a series of treatments, users’ water is obtained, and the purpose of improving the utilization rate of water resources is achieved.

Working principle of reverse osmosis system: Coagulant and multi-media filter are used to remove impurities in the boiler water, scale inhibitor is added to control the state of boiler water to avoid scale formation in water, and carbon in boiler water is cleaned and filtered by security filter and reverse osmosis chemical cleaning mechanism. Under the action of mixed bed device and regeneration device, salt in water is filtered to obtain clean user water.

The system consists of a multi-media filter, coagulant adding device, scale inhibitor adding control mechanism, security filter, reverse osmosis device, reverse osmosis chemical cleaning mechanism, carbon dioxide removal appliance, mixed bed device, and regeneration device.

Figure6 Reverse osmosis treatment flow of boiler water in the power station.

Specific process: Raw Water Tank → Raw Water → Raw Water Pump → Flocculant → Multi-Media Filter → Scale Inhibitor → Security Filter → High-Pressure Pump → Cleaning → Carbon Removal → Intermediate Water Tank → Intermediate Water Pump → Mixed Bed → Regeneration Device And Desalting Water Tank → Desalting Water Pump → User Water. In this process, a roots blower is used to remove the impurities in the air tank, and a regeneration device is constructed, which will be used as an auxiliary device for mixed bed and multi-media filter to complete the boiler water quality treatment.

Boiler water treatment project in the thermal power plant is a water treatment project that treats impurities and scales in boiler water of power station to obtain water up to standard. The water quality requirements used in this project are high, which cannot be met by traditional water quality treatment methods. NEWater uses a reverse osmosis system to purify the water source through a series of treatments such as dirt filtration so that all indexes of water quality meet the standard.

Figure7 Reverse osmosis treatment equipment for boiler water in the power station.

NEWater Practical application experiment, testing the system pretreatment device, after testing and observation, the filtration strength of the device meets the treatment requirements. For backwashing of gas, it has high filtration performance. Under the control of the reverse osmosis system, the desalination rate of boiler water is over 97.5%, which meets the requirements of boiler water treatment.

The boiler water treatment system designed by NEWater has a lower cost. In the water quality treatment of the whole project, the cost of system power consumption and equipment depreciation is high, which reduces the number of chemicals used. However, the traditional boiler water treatment equipment has high daily consumption, and the sewage treatment exceeds the standard frequently, which is not conducive to environmental protection. Therefore, whether it is cost consumption or environmental protection, the reverse osmosis system designed by NEWater has greater advantages and meets the requirements of water treatment for utility boilers.

If you have any questions with boiler water treatment, please contact NEWater. We will provide you with detailed reverse osmosis water treatment system solutions and dedicate ourselves to creating high-quality boiler make-up water, energy-saving, and emission reduction to achieve green development.

 

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