A hydrothermal integrated recovery and purification process for boiler blowdown

Abstract

The present invention provides a hydrothermal integrated recovery and purification process for boiler wastewater, which relates to the field of boiler wastewater recovery and purification. The hydrothermal integrated recovery and purification process for boiler wastewater includes the following steps: S1: surface wastewater discharge; S2: periodic wastewater discharge; S3: high-temperature vaporization desalination; S4: three-stage filtration; and S5: steam utilization. The boiler wastewater is vaporized using the power plant's existing high-temperature steam source, and crystallization is carried out using the different solubilities of various salts in water and steam. Impurities and salts dissolved in the wastewater are crystallized into solids and then enter a high-temperature desalination purification device. Through three-stage filtration and adsorption, the system desalination rate is above 90%, ensuring that the steam quality meets the requirements. Furthermore, by performing high-temperature desalination and purification on the wastewater, 100% of the heat and medium of the boiler high-temperature wastewater are recovered and converted into high-quality steam for use, achieving the dual benefits of energy conservation and saving desalted water.

Description

Technical Field

[0001] The present invention relates to the field of boiler wastewater recovery and purification, and in particular to a water-heat integrated recovery and purification process for boiler wastewater. Background Art

[0002] Boiler blowdown is the continuous or periodic removal of boiler water contaminated by salt and slag. Feedwater entering the steam drum always contains a certain amount of salt. After chemical treatment within the boiler, scaling substances in the water are converted to slag. Furthermore, the corrosion of metals by the water also produces corrosion products. Consequently, the boiler water contains various soluble and insoluble impurities. During boiler operation, only a small portion of these impurities is carried away by the steam, while the vast majority remain in the water. As the water evaporates, the concentration of these impurities gradually increases. Excessive impurity concentrations in the boiler water not only affect steam quality but can also cause scaling and corrosion on heating surfaces, compromising safe boiler operation. To control boiler water quality, boiler blowdown is necessary to remove some of the water contaminated by salt and slag and replenish it with clean feedwater.

[0003] The quality of boiler wastewater varies depending on the type of boiler and the requirements for boiler water. Generally speaking, according to the water quality requirements for industrial boiler water, it includes the following characteristics: (1) high water temperature, belonging to softened water; (2) no suspended matter or oil; (3) low salt content, dissolved oxygen content, iron, copper, and free chlorine content; (4) pH value (25℃) is about 9 to 10.5; (5) phosphate dosing is used to control the phosphate content within 30mg / L. Compared with some raw water, the water quality of these so-called "wastewater" is still very good and has good recycling value. However, the full recovery and utilization of low-grade waste heat has always been a problem that has plagued the energy-saving industry. The low recovery rate and low utilization are the current common situation in the industry. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the present invention provides a water-heat integrated recovery and purification process for boiler wastewater, which solves the problem of low recovery rate when recycling boiler wastewater.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solutions: a water-heat integrated recovery and purification process for boiler wastewater, comprising the following steps:

[0006] S1: Surface drainage

[0007] The sewage with high salinity and alkali concentration at the bottom of the boiler is continuously sent to the continuous expansion tank through the continuous main pipe to reduce the salt content, alkali content, silicate content and suspended slag content in the boiler water;

[0008] S2: Regular sewage discharge

[0009] After surface drainage, the slag and soft sediment formed after phosphate treatment accumulated at the bottom of the continuous expansion vessel and the lower header of the water-cooled wall are collected in the fixed expansion vessel and discharged into the sewer or ditch;

[0010] S3: High temperature vaporization desalination

[0011] Wastewater with low salinity and alkali concentrations flows through another pipeline into the high-temperature sewage discharge device, which uses the power plant's existing high-temperature steam source to vaporize the boiler sewage with enthalpy difference compensation, and most of the impurities and salts in the sewage will crystallize out.

[0012] S4: Three-stage filtration

[0013] After vaporization, the sewage enters a three-stage filtration system for further purification. The first stage is precision filtration, which uses a high-temperature resistant precision filter to filter suspended solids from the sewage. The second stage is barrier filtration, which reduces the steam flow rate through an ultra-large expansion chamber and sets a barrier device in the chamber to prevent vaporized precipitates from being carried out with the steam. The third stage is adsorption filtration. The main equipment of the filtration system is an adsorption filter element made of amino composite nanomaterials, a high-tech purification material and technology independently developed by our company, which has a high adsorption rate for phosphates.

[0014] S5: Steam Utilization

[0015] The qualified steam obtained through the purification steps above can directly enter the heat pump system and the unit low-temperature heater system heating network through the steam pipeline for utilization.

[0016] Preferably, the sewage discharge methods of the continuous and fixed-discharge expansion vessels in step S1 and step S2 include flash evaporation recovery and heat exchanger recovery. The recovery rate of flash evaporation sewage is only 10%-15%, while the heat recovery rate of the heat exchanger can reach about 50%, but the heat quality is reduced and it cannot be used without sufficient cold source.

[0017] Preferably, in step S3, the existing high-temperature heat source of the power plant used includes steam turbine extraction and exhaust steam, etc.

[0018] The present invention provides a water-heat integrated recovery and purification process for boiler wastewater, which has the following beneficial effects:

[0019] 1. The present invention uses the existing high-temperature steam source of the power plant to vaporize the boiler wastewater, so that the impurities and salts dissolved in the wastewater are crystallized into solids, and then enter the high-temperature desalination purification device. After three-stage filtration and adsorption, the system desalination rate is above 90%, ensuring that the steam quality meets the requirements.

[0020] 2. This invention achieves 100% recovery of the heat and medium from the boiler's high-temperature blowdown by combining high-temperature desalination and purification of low-concentration wastewater with continuous and fixed discharge of high-concentration wastewater. This heat and medium are then converted into high-quality steam, achieving the dual benefits of energy conservation and desalination. Furthermore, the bypass design enables fully automated, unattended operation, ensuring safety and reliability without disrupting normal production or safety. Furthermore, the lack of moving parts makes maintenance and repair easy. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the process flow of the present invention. DETAILED DESCRIPTION

[0022] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0023] Example:

[0024] like Figure 1 As shown, an embodiment of the present invention provides a water-heat integrated recovery and purification process for boiler wastewater, comprising the following steps:

[0025] S1: Surface drainage

[0026] The high-salinity and high-alkali concentration wastewater at the bottom of the boiler is continuously sent to the continuous expansion tank through the continuous main pipe to reduce the salt, alkali, silicate and suspended slag content in the boiler water. The high-salinity and high-alkali concentration wastewater is generally located at the bottom. Because this wastewater affects the steam quality and is prone to scaling on the inner wall of the heating surface tubes in the furnace, affecting the safe operation of the boiler, this high-salinity and high-alkali concentration wastewater needs to be recovered and discharged using traditional continuous expansion methods.

[0027] S2: Regular sewage discharge

[0028] After surface drainage, the slag and soft sediment formed after phosphate treatment accumulated at the bottom of the continuous expansion vessel and the lower header of the water-cooled wall are collected in the fixed-drain expansion vessel and discharged into the sewer or ditch. Regular drainage is the best way to discharge the waste slag and sediment accumulated at the bottom. However, regular drainage cannot be carried out frequently, as it will affect the working efficiency of the boiler.

[0029] S3: High temperature vaporization desalination

[0030] Wastewater with low salinity and alkali concentrations flows through another pipeline into a high-temperature sewage discharge device. This device uses the power plant's existing high-temperature steam source to vaporize the boiler sewage after enthalpy difference compensation. Most of the impurities and salts in the sewage will crystallize out. This is achieved by taking advantage of the different solubility of various salts in water and steam. High temperature converts water into steam, and the solubility of various salts in steam is much lower than that in water, so these salts will crystallize out.

[0031] S4: Three-stage filtration

[0032] After vaporization, the sewage enters the three-stage filtration system for further purification. The first stage is precision filtration, which uses a high-temperature resistant precision filter to filter suspended solids from the sewage. The second stage is barrier filtration, which reduces the steam flow rate through an ultra-large expansion chamber and sets a barrier device in the chamber to prevent vaporized precipitates from being carried out with the steam. The third stage is adsorption filtration. The main equipment of the filtration system is the adsorption filter element made of amino composite nanomaterials, a high-tech purification material and technology independently developed by our company. It has a high adsorption rate for phosphates. Through the adsorption effect of the adsorption filter element on salts, the residual salt substances in the steam can be further recovered, achieving a high recovery rate of salt substances and further improving the high quality of the steam.

[0033] S5: Steam Utilization

[0034] The qualified steam obtained through the purification steps above can directly enter the heat pump system and the unit low-temperature heater system heating network through the steam pipeline for utilization. The waste heat carried by the purified steam can enter the heating network for utilization, so that the heat generated by the boiler operation can be fully utilized, avoiding the waste of heat caused by boiler sewage discharge.

[0035] In step S1 and step S2, the sewage discharge methods of the continuous and fixed-drain expansion tanks include flash evaporation recovery and heat exchanger recovery. The recovery rate of sewage recovered by flash evaporation is only 10%-15%, while the heat recovery rate of the heat exchanger can reach about 50%, but the heat quality is reduced and it cannot be used without sufficient cold source. It is obvious that the waste of salts and heat in the sewage is caused by using the continuous and fixed-drainage sewage discharge methods alone.

[0036] In step S3, the existing high-temperature heat sources of the power plant used include steam turbine extraction and exhaust, etc. By achieving efficient utilization of the heat source and reducing carbon emissions, the requirements of energy conservation and emission reduction can be met.

[0037] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A hydrothermal integrated recovery and purification process for boiler wastewater, characterized by: The following steps are involved: S1: Surface drainage The sewage with high salinity and alkali concentration at the bottom of the boiler is continuously sent to the continuous expansion tank through the continuous main pipe to reduce the salt content, alkali content, silicate content and suspended slag content in the boiler water; S2: Regular sewage discharge After surface drainage, the slag and soft sediment formed after phosphate treatment accumulated at the bottom of the continuous expansion vessel and the lower header of the water-cooled wall are collected in the fixed expansion vessel and discharged into the sewer or ditch; S3: High temperature vaporization desalination Wastewater with low salinity and alkali concentrations flows through another pipeline into the high-temperature sewage discharge device, which uses the power plant's existing high-temperature steam source to vaporize the boiler sewage with enthalpy difference compensation, and most of the impurities and salts in the sewage will crystallize out. S4: Three-stage filtration After vaporization, the sewage enters a three-stage filtration system for further purification. The first stage is precision filtration, which uses a high-temperature resistant precision filter to filter suspended solids from the sewage. The second stage is barrier filtration, which reduces the steam flow rate through an ultra-large expansion chamber and sets a barrier device in the chamber to prevent vaporized precipitates from being carried out with the steam. The third stage is adsorption filtration. The main equipment of the filtration system is an adsorption filter element made of amino composite nanomaterials, a high-tech purification material and technology independently developed by our company, which has a high adsorption rate for phosphates. S5: Steam Utilization The qualified steam obtained through the purification steps above can directly enter the heat pump system and the unit low-temperature heater system heating network through the steam pipeline for utilization.

2. The hydrothermal integrated recovery and purification process for boiler wastewater according to claim 1, characterized in that: The sewage discharge methods of the continuous and fixed-discharge expansion vessels in step S1 and step S2 include flash evaporation recovery and heat exchanger recovery. The recovery rate of flash evaporation sewage is only 10%-15%, while the heat recovery rate of the heat exchanger can reach about 50%, but the heat quality is reduced and it cannot be used without sufficient cold source.

3. The hydrothermal integrated recovery and purification process for boiler wastewater according to claim 1, characterized in that: In step S3, the existing high-temperature heat sources of the power plant used include steam turbine extraction and exhaust steam.

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