Heterogeneous catalytic oxidation process and system for treating organic wastewater

Abstract

The invention relates to the technical field of industrial wastewater treatment, in particular to a heterogeneous catalytic oxidation process and system for treating organic wastewater. The heterogeneous catalytic oxidation system for treating the organic wastewater comprises an acid adjusting unit, a booster pump, a catalytic oxidation reaction unit and a pH callback pipeline mixer which are communicated in sequence, the catalytic oxidation reaction unit comprises a plurality of heterogeneous catalytic oxidation reactors which are connected in series, and the treatment temperatures and the treatment pressures of the heterogeneous catalytic oxidation reactors are sequentially reduced along the flowing direction of wastewater. The heterogeneous catalytic oxidation reactors connected in series in the system provided by the invention do not need to be pressurized step by step, are simple and efficient, and have feasibility. The heterogeneous catalytic oxidation reactors are adopted, so that the loss of the catalyst can be avoided, the continuous addition of the catalyst is not needed, the operation cost is reduced, meanwhile, the function of configuring different catalysts in each stage of heterogeneous catalytic oxidation reactor can be realized, and the degradation degree of organic matters and the precise regulation and control of each stage of target products are realized.

Description

Technical Field

[0001] The present invention relates to the technical field of industrial wastewater treatment, and particularly relates to a multiphase catalytic oxidation process and system for treating organic wastewater. Background Art

[0002] Catalytic wet air oxidation refers to a method in which, under high temperature (180°C - 280°C) and high pressure (2 - 9 MPa) conditions, oxygen in the air is used as an oxidant (other oxidants such as ozone and hydrogen peroxide can also be used), and under the action of a catalyst, dissolved or suspended organic substances or reduced inorganic substances in water are oxidized to harmless substances such as CO 2 , H 2 O, N 2 and so on. Compared with traditional physical, chemical, and biological treatment methods, this method has the advantages of high efficiency and small floor area, and is particularly suitable for the treatment of high-concentration and difficult-to-degrade organic wastewater. However, although the catalytic wet air oxidation method has many advantages, there are still some challenges and limitations in the actual application process, mainly manifested in: this technology has high requirements for reaction conditions and needs to be carried out under high temperature and high pressure environments, which not only increases the equipment investment and operation costs, but also improves the operation difficulty and safety risks. At the same time, the energy consumption during the reaction process is large, resulting in a large amount of energy waste; in addition, the catalysts used have high prices, poor stability, are easy to disintegrate, and have short service lives. At the same time, there are problems such as the need for excessive dosing of oxidants (such as hydrogen peroxide) and low utilization rates.

[0003] In this regard, Chinese Patent Document CN107572651B discloses a method and device for treating industrial wastewater by multi-stage wet oxidation. Although it reduces energy consumption and treatment costs to a certain extent, the researchers of the present invention found that the setting of gradually increasing the temperature of the wastewater from the first-stage oxidation reactor to the third-stage oxidation reactor is difficult to implement in engineering. Specifically, it is known to those skilled in the art that "under a standard atmospheric pressure, the boiling point of water is 100 °C. If the water temperature is to be raised above 100 °C, the pressure must be correspondingly increased." Therefore, in its setting, the pressure of the first-stage oxidation reactor to the third-stage oxidation reactor will inevitably increase in sequence. However, the wastewater to be treated cannot flow from a low-pressure area to a high-pressure area by itself. If it is to be implemented according to the disclosed scheme, a booster pump must be set in front of each oxidation reactor. However, when the booster pump pumps water from a low-pressure reactor into a high-pressure reactor, the inlet of the booster pump is in a situation of high water temperature (especially when the water temperature is above 100 °C) and low pressure, and cavitation is very likely to occur, causing damage to the booster pump and unable to operate normally. In addition, the researchers also found that it uses a homogeneous form to add the catalyst, that is, the catalyst is prepared into a solution and added to the wastewater to be treated, and after flowing through the first, second, and third multi-phase catalytic oxidation reactors, it is discharged from the system in the form of precipitated sludge; this not only results in a large amount of consumption or loss of the catalyst, but also requires continuous addition of the catalyst. Therefore, there is an urgent need to provide a multi-phase catalytic oxidation system for treating organic wastewater that is easy to implement in engineering and does not require continuous addition of the catalyst. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defects that the existing multi-phase catalytic oxidation system for treating organic wastewater is difficult to implement in engineering, requires continuous addition of the catalyst, and has high operating costs, so as to provide a multi-phase catalytic oxidation process and system for treating organic wastewater to solve the above problems.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] In the first aspect, the present invention provides a multi-phase catalytic oxidation system for treating organic wastewater, which includes an acid adjustment unit, a booster pump, a catalytic oxidation reaction unit, and a pH callback pipe mixer connected in sequence; the catalytic oxidation reaction unit includes a plurality of multi-phase catalytic oxidation reactors connected in series and with the treatment temperature and treatment pressure decreasing in sequence along the flow direction of the wastewater; in the present invention, the multi-phase catalytic oxidation reactor is a reactor having a filling area for filling solid catalysts (for example, a fixed-bed reactor, and the conventional structure will not be described in detail), that is, the multi-phase catalytic oxidation reactor is filled with solid catalysts, and the solid catalysts exist as the core functional unit of the multi-phase catalytic oxidation reactor to contact the solid catalyst with liquid or gas reactants to achieve catalytic conversion reactions; there is no booster pump between two adjacent multi-phase catalytic oxidation reactors in the catalytic oxidation reaction unit.

[0007] Among them, the acid adjustment unit is used to connect to the inlet pipeline of the wastewater to be treated and adjust the acidity.

[0008] The booster pump is used to boost the pressure of the wastewater in the acid adjustment unit.

[0009] The catalytic oxidation reaction unit is used to carry out catalytic oxidation reaction on the heated wastewater.

[0010] The pH callback pipe mixer is used to add alkali to the wastewater after the catalytic oxidation reaction unit to carry out pH callback.

[0011] Preferably, the acid adjustment unit includes a pH adjustment pipe mixer and an inlet adjustment tank connected in sequence; among them, the pH adjustment pipe mixer includes a mixer body, an acid liquid inlet, a wastewater inlet and a mixed liquid outlet arranged on the mixer body, and is used to adjust the pH of the wastewater by adding acid; the inlet adjustment tank includes a storage tank communicated with the mixed liquid outlet, an on-line pH meter arranged in the storage tank, the storage tank is used to store the wastewater after being adjusted by adding acid by the pH adjustment pipe mixer, and the on-line pH meter in the storage tank is used to ensure the stability of the inlet pH.

[0012] And / or, a preheating heat exchanger for heat exchange with the outlet material of the catalytic oxidation reaction unit is also provided between the booster pump and the catalytic oxidation reaction unit; among them, the cold side of the preheating heat exchanger is communicated with the outlet of the booster pump and the inlet of the catalytic oxidation reaction unit, and the hot side of the preheating heat exchanger is communicated with the outlet of the catalytic oxidation reaction unit; that is, the cold side passes through the raw wastewater, and the hot side passes through the outlet water of the multiphase catalytic oxidation reactor, realizing the recycling of heat. The above temperature control depends on the operating temperature required for the catalytic oxidation reaction; optionally, the preheating heat exchanger includes, but is not limited to, one of heat exchangers suitable for high temperature and high pressure, easy fouling and other occasions, such as plate heat exchangers, shell-and-tube heat exchangers, spiral plate heat exchangers, etc.

[0013] And / or, when the oxidant participating in the catalytic oxidation reaction in the catalytic oxidation reaction unit is a non-gaseous oxidant, at least a non-gaseous oxidant dosing pipe mixer is provided at the inlet of the first multiphase catalytic oxidation reactor where the treatment temperature and treatment pressure decrease in sequence along the wastewater flow direction, and a non-gaseous oxidant dosing port is arranged on the non-gaseous oxidant dosing pipe mixer; when using non-gaseous oxidants such as hydrogen peroxide, the non-gaseous oxidant dosing pipe mixer can be only arranged at the inlet of the first multiphase catalytic oxidation reactor, and preferably, a non-gaseous oxidant dosing pipe mixer is arranged at the inlet of each multiphase catalytic oxidation reactor.

[0014] And / or, when the oxidant participating in the catalytic oxidation reaction in the catalytic oxidation reaction unit is a gaseous oxidant, a gaseous oxidant injection port is provided at the bottom of each multiphase catalytic oxidation reactor for injecting the gaseous oxidant into the wastewater to be treated. When using gaseous oxidants such as oxygen or air, a gaseous oxidant injection port needs to be provided at the bottom of each multiphase catalytic oxidation reactor.

[0015] Preferably, the catalytic oxidation reaction unit includes 2 - 4 serially connected multiphase catalytic oxidation reactors, preferably composed of 3 serially connected multiphase catalytic oxidation reactors; according to the types and degradation rules of characteristic organic pollutants in the wastewater, determine the reaction stage. Generally, the stage number N is taken as 2 - 4 stages. For each stage of multiphase catalytic oxidation reactor, a catalyst with higher efficiency is preferably selected, and the single-stage reaction time and catalyst filling amount are determined according to the degradation rate of each stage of multiphase catalytic oxidation reactor.

[0016] And / or, there is no booster pump between the multiphase catalytic oxidation reactors in the catalytic oxidation reaction unit.

[0017] And / or, an on-line thermometer and an on-line pressure gauge are also provided in each multiphase catalytic oxidation reactor in the catalytic oxidation reaction unit.

[0018] And / or, an on-line oxidant concentration meter is also provided in each multiphase catalytic oxidation reactor in the catalytic oxidation reaction unit. An on-line oxidant concentration meter and an oxidant dosing point are set at the inlet of each stage of multiphase catalytic oxidation reactor for staged dosing as required, and the distribution ratio can be adjusted according to the consumption of oxidant in each stage.

[0019] Preferably, a heater is provided at the inlet of at least the first multiphase catalytic oxidation reactor along the wastewater flow direction in the catalytic oxidation reaction unit for heating the wastewater; the heater can be provided only at the inlet of the first multiphase catalytic oxidation reactor, and preferably, a heater is provided at the inlet of each multiphase catalytic oxidation reactor.

[0020] And / or, an on-line pH meter is also provided in the pH callback pipe mixer; the pH callback pipe mixer is used to adjust the pH of the wastewater after catalytic oxidation treatment to neutral. The on-line pH meter is set to ensure the stability of the effluent pH.

[0021] And / or, a final cooling heat exchanger for heat exchange with circulating cooling water is further provided in front of the pH callback pipeline mixer, which is used to exchange heat between the effluent of the catalytic oxidation reaction unit and the circulating cooling water to reduce the temperature; optionally, the final cooling heat exchanger includes, but is not limited to, one of heat exchangers suitable for high temperature and high pressure, easy scaling and other occasions such as plate heat exchangers, shell-and-tube heat exchangers, spiral plate heat exchangers, etc.; the final cooling heat exchanger is set according to the specific situation of the project. If it directly enters the evaporation crystallization device at the back end, it may not be set. If it is also connected to other process units at the back end, the heat exchanger parameters need to be selected according to the inlet water temperature requirements of the back-end process.

[0022] Preferably, the heater is a raw water heater; the raw water heater is a device that directly mixes steam with water to heat the water, and its thermal efficiency is more than 98%. The steam and the wastewater after heating are mixed through the raw water heater and heated to the temperature required for the catalytic oxidation reaction; the steam is saturated steam, which meets the temperature and pressure requirements of the multiphase catalytic oxidation reactor, and the steam pressure is 0.8-1.8 MPa;

[0023] And / or, when the oxidant participating in the catalytic oxidation reaction in the catalytic oxidation reaction unit is a gaseous oxidant, a gas-liquid separator is further provided behind the final cooling heat exchanger, which is used for gas-liquid separation of the effluent of the final cooling heat exchanger. Specifically, if gaseous oxidants such as oxygen or air are used in the catalytic oxidation reaction unit, a gaseous separator needs to be set after the final cooling heat exchanger; however, if a non-gaseous oxidant (such as hydrogen peroxide, added in the form of hydrogen peroxide liquid) is used, a gas-liquid separator does not need to be set.

[0024] In a second aspect, the present invention also provides a multiphase catalytic oxidation process for treating organic wastewater, which uses the above-mentioned multiphase catalytic oxidation system for treating organic wastewater to degrade the organic wastewater.

[0025] Preferably, the specific treatment process of the multiphase catalytic oxidation process includes: introducing the wastewater to be treated into the acid adjustment unit through the wastewater inlet pipeline to be treated, and adding acid to adjust the pH of the wastewater to be treated; the wastewater after acid addition and adjustment is pressurized by a booster pump and then flows through the catalytic oxidation reaction unit and the pH callback pipeline mixer in sequence and then discharges water.

[0026] Preferably, the wastewater after being pressurized by the booster pump also flows through a preheating heat exchanger to exchange heat with the effluent of the catalytic oxidation reaction unit to increase the temperature; after flowing through the preheating heat exchanger, the effluent of the catalytic oxidation reaction unit also flows through a final cooling heat exchanger for heat exchange and temperature reduction again; the effluent of the catalytic oxidation reaction unit enters the hot side of the preheating heat exchanger as a heat source, exchanges heat with the raw water after passing through the booster pump to reduce the temperature, and then enters the hot side of the final cooling heat exchanger to exchange heat with the circulating cooling water for temperature reduction again to meet the inlet water temperature requirements of the subsequent process units; when using a gaseous oxidant, the wastewater after the heat exchange and temperature reduction again also flows through a gas-liquid separator for gas-liquid separation;

[0027] And / or, when using a non-gaseous oxidant, the non-gaseous oxidant is added (when using a non-gaseous oxidant) or / and heating is carried out at the inlet of the first multiphase catalytic oxidation reactor where the temperature and treatment pressure of the wastewater decrease successively along the wastewater flow direction at least in the catalytic oxidation reaction unit; Optionally, the non-gaseous oxidant includes hydrogen peroxide;

[0028] And / or, when using a gaseous oxidant, a gaseous oxidant injection port is provided at the bottom of each multiphase catalytic oxidation reactor in the catalytic oxidation reaction unit; Optionally, the gaseous oxidant is an oxygen-containing gas, and the oxygen-containing gas includes air or / and oxygen.

[0029] Preferably, the temperature of the first multiphase catalytic oxidation reactor in the direction of the wastewater to be treated is 160 - 200 °C, and the pressure mainly ensures that the wastewater is in a liquid phase at this temperature. The reaction pressure is controlled according to the reaction temperature, and the pressure is 0.8 - 1.8 MPa. The temperature loss between two adjacent multiphase catalytic oxidation reactors is controlled below 20 °C, and the temperature of the effluent from the entire catalytic oxidation reaction unit is controlled above 80 °C;

[0030] And / or, the residence time of the first multiphase catalytic oxidation reactor in the catalytic oxidation reaction unit is 10 - 30 min, and the total residence time of the entire catalytic oxidation reaction unit is 60 - 120 min. This is because the reaction in the first-stage multiphase catalytic oxidation reactor is rapid, and the residence time is taken as 10 - 30 min. Then, according to the project treatment scale and the law of organic matter decomposition, the residence time of each stage is determined, and the total residence time is 60 - 120 min.

[0031] Preferably, the acid used in the acid adjustment unit includes sulfuric acid or / and hydrochloric acid;

[0032] And / or, the pH of the wastewater after acid addition adjustment is 2 - 4;

[0033] And / or, the head of the booster pump is set to 80 - 180 m, and frequency conversion control is used to adjust the inlet water pressure and flow rate;

[0034] And / or, the catalyst in the catalytic oxidation reaction unit includes, but is not limited to, at least one of a targeted catalyst for treating wastewater containing heterocyclic compounds, a targeted catalyst for treating wastewater containing aromatic compounds, and a targeted catalyst for treating wastewater containing hydrocarbons; the solid catalysts in each stage of the multiphase catalytic oxidation reactor are determined according to the characteristics of the wastewater quality and the reaction parameters controlled at each stage to determine the type and filling parameters of the catalyst. For the wastewater quality to be treated in the present invention, the catalyst is preferably a catalyst independently developed by the applicant, including a targeted catalyst for treating wastewater containing heterocyclic compounds (CN201610217796.5), a targeted catalyst for treating wastewater containing aromatic compounds (CN201610217797.X), a targeted catalyst for treating wastewater containing hydrocarbons (CN201610218965.7), and one or several of various commercially available catalysts, which reduces the reaction activation energy, thereby reducing the reaction temperature and pressure, making the reaction conditions milder, and can achieve precise control of the degree of organic matter degradation and the target products at each stage according to the actual treatment requirements;

[0035] And / or, the alkali used in the pH callback pipe mixer includes sodium hydroxide.

[0036] In the present invention, the wastewater to be treated is high-concentration and difficult-to-degrade organic wastewater, specifically referring to the high-concentration membrane concentrate obtained after the biochemical and advanced treatment of industrial wastewater, which has the characteristics of high salt content, high content of difficult-to-degrade organic matter, and complex composition. Its conventional water quality situation is that the COD is about 800 - 2500 mg / L, the TDS is about 35000 - 150000 mg / L, and after the front-end process treatment, most of the COD is difficult-to-degrade organic matter with relatively stable structures, such as heterocyclic compounds, benzene series, halogenated hydrocarbons, hydrocarbons (cyclic hydrocarbons, chain hydrocarbons, etc.). Since H 2 O 2 has higher oxidation ability than air / oxygen, it can oxidize organic matter more thoroughly. Therefore, the oxidant is preferably H 2 O 2 . When using hydrogen peroxide as the oxidant, the dosage of H 2 O 2 is added at 3 - 8 times the COD concentration, and industrial 27.5% hydrogen peroxide is used. When using oxygen-containing gas as the oxidant, the dosage of O 2 is added at 2 - 10 times the COD concentration.

[0037] In the present invention, the multiphase catalytic oxidation reactors are arranged in series in multiple stages, successively becoming the first-stage multiphase catalytic oxidation reactor (corresponding to the first multiphase catalytic oxidation reactor in the flowing direction of the wastewater to be treated as described above), the second-stage multiphase catalytic oxidation reactor... the N-stage multiphase catalytic oxidation reactor. The incoming water first enters the high-temperature and high-pressure first-stage multiphase catalytic oxidation reactor to obtain the effluent of reaction 1. The effluent of reaction 1 enters the medium-temperature and medium-pressure second-stage multiphase catalytic oxidation reactor to obtain the effluent of reaction 2. The effluent of reaction 2 then enters the subsequent reactors until it enters the low-temperature and low-pressure N-stage multiphase catalytic oxidation reactor to obtain the effluent of reaction N. Among them, the first-stage multiphase catalytic oxidation reactor is in a relatively high-temperature and high-pressure environment, and the reaction process is mainly the thermal decomposition stage. Under the action of high temperature and the catalyst, the macromolecular organic substances with complex structures are ring-opened and chain-broken, and are converted into compounds that are more easily decomposed. The higher the temperature in this stage, the faster the reaction rate. The temperature and pressure of the subsequent-stage multiphase catalytic oxidation reactors are reduced to a certain extent, mainly for the local oxidation process, oxidizing and decomposing the ring-opened and chain-broken organic substances into small-molecule intermediate products, and then gradually oxidizing the organic substances stage by stage until complete oxidation into carbon dioxide and water is achieved. As the degree of degradation deepens, the types of organic substances to be treated change, and the corresponding reaction activation energy also gradually decreases.

[0038] In the present invention, under the influence of factors such as the structure of the multiphase catalytic oxidation reactor (height-diameter ratio, internal components, etc.), the type and filling form of the catalyst, the operating conditions (temperature, pressure, liquid rising flow rate), the reaction heat effect (the oxidation process is an exothermic reaction, and the reaction at the bottom of the reactor is intense), heat transfer (convection, radiation, and conduction, etc.) and loss (heat exchange with the outside), and heat preservation performance, a gradient distribution from high temperature and high pressure to low temperature and low pressure is formed.

[0039] In the present invention, the filling rate of the solid catalyst in the multiphase catalytic oxidation reactor is 50% - 80% (the filling rate refers to the ratio of the catalyst volume to the total volume of the reactor);

[0040] In the present invention, because temperature and pressure are related, usually the temperature of each reactor is controlled. Once the temperature is determined, the pressure is basically determined. In addition, because no booster pump is provided and the reactors at all levels are directly connected in series, as long as the inlet water pressure is sufficient to overcome the resistance of each reactor and ensure that the water can enter and exit normally, it is okay. Therefore, usually the pressure of each staged reactor is not controlled separately.

[0041] The technical solution of the present invention has the following advantages:

[0042] 1. A multiphase catalytic oxidation system for treating organic wastewater, which system comprises an acid adjustment unit, a booster pump, a catalytic oxidation reaction unit, and a pH callback pipe mixer connected in sequence; the catalytic oxidation reaction unit comprises a plurality of multiphase catalytic oxidation reactors connected in series and with the treatment temperature and treatment pressure decreasing successively along the wastewater flow direction. In the multiphase catalytic oxidation reactor of the present invention, a multistage series arrangement is adopted. At the same time, in accordance with the catalytic wet oxidation organic matter degradation process (thermal decomposition → partial oxidation → complete oxidation) and the specific reaction condition requirements of each stage, a zoning treatment strategy in space is designed. Each stage can customize appropriate temperature and pressure conditions for specific reaction stages and thermodynamic requirements. At the same time, the series arrangement of the multiphase catalytic oxidation reactors from high temperature and high pressure to low temperature and low pressure can greatly reduce the reaction stage time at relatively high temperature and high pressure, and reduce heat dissipation; at the same time, a large amount of heat energy and oxidant released during the oxidation process can also be utilized in a gradient manner through each reaction stage; overall, the present invention enables energy to be fully utilized in the whole system, improving the energy utilization rate of the overall process. Moreover, in the multiphase catalytic oxidation system of the present invention, the multiphase catalytic oxidation reactors connected in series do not need to be pressurized step by step, which is simple and efficient, avoiding the problem that the system cannot operate due to cavitation damage of the booster pump, having feasibility, and at the same time can also achieve the purpose of following the organic matter degradation law, improving the treatment efficiency, and reducing the operation energy consumption.

[0043] In addition, compared with the addition in the form of homogeneous phase of the catalyst in the prior art (preparing a catalyst solution, adding it to the first-stage oxidation reactor, flowing continuously through the subsequent second- and third-stage oxidation reactors, flowing in continuously and flowing out continuously, and unable to achieve the function of configuring exclusive catalysts in each stage of the multiphase catalytic oxidation reactor), in the present invention, a multiphase catalytic oxidation reactor (a device for contacting a solid catalyst with a liquid or gas reactant to achieve a catalytic conversion reaction) is adopted for the catalytic oxidation reaction. The solid catalyst configured therein does not need to be continuously added in the form of a reagent and has no loss during the reaction process, reducing the operation cost. At the same time, the function of configuring different types of solid catalysts in each stage of the multiphase catalytic oxidation reactor can also be achieved. Thus, exclusive solid catalysts with higher degradation efficiency can be configured in each stage of the multiphase catalytic oxidation reactor according to the types of characteristic organic pollutants, degradation laws, and reaction conditions in the wastewater, further reducing the reaction activation energy, thereby reducing the reaction temperature and pressure, making the reaction conditions milder, and enabling precise control of the degree of organic matter degradation and the target products of each stage according to actual treatment requirements. Therefore, through the setting of the multistage multiphase catalytic oxidation reactor in the system provided by the present invention, the adaptability and flexibility of the reactor are enhanced. Each stage of the reactor can customize appropriate temperature and pressure conditions according to specific reaction stages and thermodynamic requirements, and can be customized and adjusted for different types of wastewater and treatment requirements, having broad application prospects and important market value.

[0044] 2. In the multiphase catalytic oxidation system for treating organic wastewater of the present invention, the inlet temperature of the first-stage multiphase catalytic oxidation reactor (high temperature and high pressure) is controlled at 150 - 200 °C, and the reaction temperature and pressure of the subsequent reactors are successively reduced based on those of the first-stage multiphase catalytic oxidation reactor. Compared with the reaction conditions of conventional catalytic wet oxidation (temperature 180 - 280 °C, pressure 2 - 9 MPa), the reaction temperature and pressure are significantly reduced, achieving the purpose of energy conservation and consumption reduction.

[0045] 3. In the multiphase catalytic oxidation system for treating organic wastewater of the present invention, in view of the lack of adjustment and control measures for the temperature, pressure, and oxidant dosage in each stage of the multiphase catalytic oxidation reactor in the prior art, a supplementary heater and a non-gaseous oxidant dosing pipeline mixer are provided at the inlet of each stage of the multiphase catalytic oxidation reactor. Online thermometers and online pressure gauges are respectively installed in each stage of the multiphase catalytic oxidation reactor. At the same time, an online hydrogen peroxide concentration meter is installed at the outlet of each stage of the multiphase catalytic oxidation reactor, which can control the temperature, pressure, and oxidant dosage of each stage as needed, improve the treatment efficiency, reduce the operation energy consumption and chemical consumption, and has a wider adjustment range and more flexible operation flexibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0047] Figure 1 It is a schematic diagram of the multiphase catalytic oxidation system of Embodiment 1 of the present invention;

[0048] Figure 2 It is a schematic diagram of the multiphase catalytic oxidation system of Embodiment 2 of the present invention.

[0049] Reference numerals: 1 - pH adjustment pipeline mixer, 2 - inlet adjustment tank, 3 - booster pump, 4 - preheating heat exchanger, 5 - non-gaseous oxidant dosing pipeline mixer, 6 - heater, 7 - multiphase catalytic oxidation reactor, 8 - final cooling heat exchanger, 9 - pH callback pipeline mixer, 10 - gas-liquid separator, 11 - gaseous oxidant injection port. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0050] The following embodiments are provided to better further understand the present invention. It is not limited to the best embodiment, and does not limit the content and protection scope of the present invention. Any product obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior art features that is the same or similar to the present invention falls within the protection scope of the present invention.

[0051] For those embodiments where specific experimental procedures or conditions are not indicated, the operations or conditions of the conventional experimental procedures described in the literature in this field can be followed. For reagents or instruments whose manufacturers are not indicated, they are all conventional reagent products that can be obtained through commercial purchase.

[0052] Example 1

[0053] Wastewater 1: The recovery rate of the wastewater treatment and reuse system of a certain semi-coke plant is about 95%. The COD in the final membrane concentrate is about 2200 mg / L, and the TDS is about 72000 mg / L. It is measured that the organic matter in the membrane concentrate is mainly aromatic compounds, and contains a certain amount of chromogenic group substances, as well as substances such as halogenated hydrocarbons and long-chain alkanes.

[0054] This embodiment provides a multiphase catalytic oxidation system for treating organic wastewater. The schematic structure is as Figure 1 shown. The multiphase catalytic oxidation system consists of an acid adjustment unit (composed of a pH adjustment pipeline mixer 1 and an inlet water adjustment tank 2), a booster pump 3, a preheating heat exchanger 4, a non-gaseous oxidant dosing pipeline mixer 5, a heater 6 (specifically a raw water heater), a catalytic oxidation reaction unit composed of 3 multiphase catalytic oxidation reactors 7 filled with solid catalysts (successively called the primary multiphase catalytic oxidation reactor, the secondary multiphase catalytic oxidation reactor, and the tertiary multiphase catalytic oxidation reactor) in series and gradually distributed from high temperature and high pressure to low temperature and low pressure in the flow direction of the wastewater to be treated, a final cooling heat exchanger 8, and a pH callback pipeline mixer 9. An oxidant dosing pipeline mixer 5 and a raw water heater are provided in front of each multiphase catalytic oxidation reactor.

[0055] Among them, the pH adjustment pipeline mixer 1 is used to connect the inlet pipeline of the wastewater to be treated and simultaneously adjust the pH of the wastewater by adding acid;

[0056] The inlet water adjustment tank 2 is used to store the wastewater after the pH is adjusted by adding acid by the pH adjustment pipeline mixer 1. The inlet water adjustment tank 2 is also equipped with an on-line pH meter to ensure the stability of the inlet pH;

[0057] The booster pump 3 is used to pressurize the wastewater in the acid adjustment unit;

[0058] The preheating heat exchanger 4 is specifically a plate heat exchanger, which is used to exchange heat and raise the temperature of the pressurized wastewater with the effluent of the catalytic oxidation reaction unit. Among them, the cold side of the preheating heat exchanger 4 is connected to the outlet of the booster pump 3, and the hot side of the preheating heat exchanger 4 is connected to the outlet of the catalytic oxidation reaction unit. That is, the cold side passes through the raw wastewater, and the hot side passes through the effluent of the multiphase catalytic oxidation reactor;

[0059] The non-gaseous oxidant dosing pipeline mixer 5 is used to add non-gaseous oxidant to the wastewater to be treated;

[0060] Raw water heater, used to heat the wastewater after adding non-gaseous oxidant by mixing it with steam;

[0061] Catalytic oxidation reaction unit, used to carry out catalytic oxidation reaction on the heated wastewater. In each multi-phase catalytic oxidation reactor 7 in the catalytic oxidation reaction unit, an on-line thermometer and an on-line pressure gauge are also provided. At the same time, an on-line hydrogen peroxide concentration gauge is set at the inlet of each stage of multi-phase catalytic oxidation reactor;

[0062] Final cooling heat exchanger 8, specifically a plate heat exchanger, used to further exchange heat and cool down the outlet water of the preheating heat exchanger 4 with circulating cooling water;

[0063] pH callback pipeline mixer 9, used to add alkali to the wastewater after the catalytic oxidation reaction unit to adjust the pH back to neutral. An on-line pH meter is also provided in the pH callback pipeline mixer 9 to ensure the stability of the outlet water pH.

[0064] According to the characteristic pollutants in the wastewater 1, the first-stage multi-phase catalytic oxidation reactor is filled with a targeted catalyst for treating wastewater containing aromatic compounds (CN201610217797.X) (referred to as catalyst I), and the second-stage and third-stage multi-phase catalytic oxidation reactors are filled with a targeted catalyst for treating wastewater containing hydrocarbons (CN201610218965.7) (referred to as catalyst II). The filling rate of the solid catalyst in each stage of multi-phase catalytic oxidation reactor is 68%.

[0065] This embodiment also provides the above-mentioned multi-phase catalytic oxidation process for treating organic wastewater. This process uses the above-mentioned multi-phase catalytic oxidation system for treating organic wastewater to degrade the organic wastewater in the wastewater 1. The specific steps are as follows:

[0066] The wastewater 1 is introduced into the pH adjustment pipeline mixer 1 through the pipeline for wastewater to be treated, and acid is added to adjust the pH of the wastewater to be treated. The wastewater after acid addition is stored in the inlet adjustment tank 2, and then after being pressurized by the booster pump 3, it flows through the cold side of the preheating heat exchanger 4, the non-gaseous oxidant dosing pipeline mixer 5, the raw water heater, the first-stage multi-phase catalytic oxidation reactor, the non-gaseous oxidant dosing pipeline mixer 5, the raw water heater, the second-stage multi-phase catalytic oxidation reactor, the non-gaseous oxidant dosing pipeline mixer 5, the raw water heater, the third-stage multi-phase catalytic oxidation reactor, the hot side of the preheating heat exchanger 4, the hot side of the final cooling heat exchanger 8, and the pH callback pipeline mixer 9 in sequence, and then is discharged.

[0067] The main control parameters are:

[0068] Hydrochloric acid is added to the inlet water to adjust the pH to 3.0, and it is collected in the inlet adjustment tank;

[0069] The inlet water temperature is about 170 °C, the average temperature loss per stage is about 15 °C, and the outlet temperature is about 120 °C;

[0070] If the inlet water pressure is about 1.0 MPa, the head of the booster pump is set to 100 m, with variable frequency control, and 1.0 MPa saturated steam is used.

[0071] Retention time: The retention time of the first-stage multiphase catalytic oxidation reactor is 20 min, the retention time of the second-stage multiphase catalytic oxidation reactor is 40 min, the retention time of the third-stage multiphase catalytic oxidation reactor is 40 min, and the total retention time is 100 min.

[0072] H 2 O 2 Dosage: It is 5 times the COD concentration, and it is added in stages. According to the online hydrogen peroxide concentration meter at the outlet, the distribution ratio is adjusted. Among them, the dosage in the first-stage reaction is about 50% of the total H 2 O 2 dosage, the dosage in the second-stage reaction is about 50% of the total H 2 O 2 dosage, and no addition is made in the third-stage reaction.

[0073] After the effluent of the third-stage multiphase catalytic oxidation reactor is heat-exchanged and adjusted to neutral pH with sodium hydroxide, the final effluent COD ≤ 50 mg / L, the removal rate exceeds 97%, and there is no catalyst loss. There is no need to continuously add catalyst, and there is no cavitation phenomenon in the booster pump.

[0074] Example 2

[0075] Wastewater 2: A coal gasification wastewater treatment system uses a membrane method for salt separation and zero discharge. After multi-stage concentration and nanofiltration for salt separation, the COD in the nanofiltration concentrate side (Na 2 SO 4 side) is about 1200 mg / L, and the TDS is about 126000 mg / L. It is determined that the membrane concentrate mainly consists of heterocyclic compounds and contains a small amount of halogenated hydrocarbons, long-chain alkanes and other substances.

[0076] The multiphase catalytic oxidation system for treating organic wastewater in this example is the same as that in Example 1.

[0077] Based on the above water quality characteristics of wastewater 2, the first-stage multiphase catalytic oxidation reactor is filled with a targeted catalyst for treating wastewater containing heterocyclic compounds (ZL201610217796.5) (referred to as catalyst III), and the second-stage and third-stage multiphase catalytic oxidation reactors are filled with targeted catalysts for treating wastewater containing hydrocarbons (CN201610218965.7) (referred to as catalyst II). The filling rate of the solid catalyst in each multiphase catalytic oxidation reactor is 73%.

[0078] This example provides a multiphase catalytic oxidation process for treating organic wastewater. The difference between this process and that in Example 1 is that the main control parameters are:

[0079] Adjust the pH of the influent to 3.5 by adding sulfuric acid, and collect it in the influent adjustment tank;

[0080] The influent temperature is about 150 °C, the single-stage temperature loss is about 12 °C, and the outlet temperature is about 115 °C.

[0081] The influent pressure is about 0.8 MPa. Then, set the head of the booster pump to 80 m, with variable frequency control. The steam uses 0.8 MPa saturated steam.

[0082] Retention time: The retention time of the first-stage multiphase catalytic oxidation reactor is 15 min, the retention time of the second-stage multiphase catalytic oxidation reactor is 30 min, the retention time of the third-stage multiphase catalytic oxidation reactor is 30 min, and the total retention time is 75 min.

[0083] H 2 O 2 Dosage: It is 4 times the COD concentration, and it is added in stages. According to the online hydrogen peroxide concentration meter at the outlet, adjust the distribution ratio. Among them, the dosage in the first-stage reaction is 60% of the total H 2 O 2 dosage, the dosage in the second-stage reaction is 40% of the total H 2 O 2 dosage, and no addition in the third-stage reaction.

[0084] After the effluent of the third-stage multiphase catalytic oxidation reactor is heat-exchanged and the pH is adjusted to neutral by adding sodium hydroxide, the final effluent COD ≤ 30 mg / L, the removal rate exceeds 97%, and there is no catalyst loss. There is no need to continuously add the catalyst, and there is no cavitation phenomenon in the booster pump.

[0085] Example 3

[0086] This example provides a multiphase catalytic oxidation system for treating organic wastewater. The schematic structure is as Figure 2 shown. The difference between this multiphase catalytic oxidation system and that of Example 1 is that all non-gaseous oxidant dosing pipeline mixers 5 are removed. Gas-phase oxidant injection ports 11 are provided at the bottoms of the multiphase catalytic oxidation reactors 7 (the first-stage multiphase catalytic oxidation reactor, the second-stage multiphase catalytic oxidation reactor, and the third-stage multiphase catalytic oxidation reactor) for injecting oxygen (O 2 (dosage is 5 times the COD concentration)) into the wastewater to be treated. A gas-liquid separator 10 is also provided after the final cooling heat exchanger 8 for gas-liquid separation of the effluent of the final cooling heat exchanger 8. Other conditions are the same as those in Example 1.

[0087] After the effluent of the third-stage multiphase catalytic oxidation reactor is heat-exchanged and the pH is adjusted to neutral by adding sodium hydroxide, the final effluent COD ≤ 40 mg / L, the removal rate exceeds 97%, and there is no catalyst loss. There is no need to continuously add the catalyst, and there is no cavitation phenomenon in the booster pump.

[0088] Comparative Example 1

[0089] This comparative example provides a catalytic oxidation system for treating organic wastewater to treat Wastewater 1. The difference between this catalytic oxidation system and Example 1 is that the catalytic oxidation reaction unit only contains 1 multiphase catalytic oxidation reactor 7, and the catalyst uses a targeted catalyst for treating wastewater containing heterocyclic compounds (ZL201610217796.5) (referred to as Catalyst III);

[0090] The main control parameters are as follows:

[0091] Hydrochloric acid is added to the influent to adjust the pH to about 3.0 and collected in the influent adjustment tank;

[0092] The influent temperature is about 200 °C and the outlet temperature is about 180 °C.

[0093] The influent pressure is about 1.6 MPa, the head of the booster pump is set to 160 m, frequency conversion control is used, and 1.6 MPa saturated steam is used for the steam.

[0094] Residence time: 120 min.

[0095] H 2 O 2 Dosage: 5 times the COD concentration.

[0096] Other conditions are the same as those in Example 1. After the effluent is heat-exchanged and sodium hydroxide is added to adjust the pH to neutral, the final effluent COD ≤ 150 mg / L and the removal rate is about 93%.

[0097] Even if the reaction temperature increases, the reaction pressure increases, and the residence time increases, there is still a certain gap in the COD removal ability and the degree of organic matter degradation compared with Example 1 of the present invention.

[0098] Comparative Example 2

[0099] This comparative example provides a catalytic oxidation system for treating organic wastewater. The difference between this comparative example and Example 1 is that a homogeneous catalytic reactor (without solid catalyst in the reactor) is used for the catalytic oxidation reaction. That is, the catalyst (ferrous sulfate, dosage is 6 mmol / L) is prepared into a solution and continuously added to the wastewater to be treated. After flowing through the first, second, and third stage catalytic oxidation reactors, it is discharged from the system in the form of precipitated sludge. Moreover, the catalytic oxidation reactors 7 are gradually distributed from low temperature and low pressure to high temperature and high pressure in the flowing direction of the wastewater to be treated. That is, booster pumps 3 are added between the first stage catalytic oxidation reactor, the second stage catalytic oxidation reactor, and the third stage catalytic oxidation reactor. At the same time, by controlling the raw water heater, the temperatures of the influent water of the first stage catalytic oxidation reactor, the influent water of the second stage catalytic oxidation reactor, and the effluent water of the third stage catalytic oxidation reactor are controlled at 90 °C, 190 °C, and 240 °C respectively, and other conditions are the same as those in Example 1. During the implementation of this comparative example, due to the problem of cavitation of the booster pump, the booster pump was damaged, resulting in the system being unable to operate normally, and the catalyst needs to be continuously added, with high operating costs.

[0100] Obviously, the above embodiments are only examples clearly described and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or variations derived therefrom are still within the protection scope of the present invention.

Claims

1. A heterogeneous catalytic oxidation system for treating organic wastewater, characterized in that: The system comprises an acid adjustment unit, a booster pump (3), a catalytic oxidation reaction unit, and a pH adjustment pipeline mixer (9) which are connected in sequence; the catalytic oxidation reaction unit comprises a plurality of multiphase catalytic oxidation reactors (7) which are connected in series and whose treatment temperature and treatment pressure decrease in sequence along the flow direction of the wastewater.

2. The multiphase catalytic oxidation system according to claim 1, characterized in that: The acid adjustment unit comprises a pH adjustment pipeline mixer (1) and a water inlet adjustment tank (2) which are connected in sequence; wherein the pH adjustment pipeline mixer (1) comprises a mixer body, and an acid liquid inlet, a wastewater inlet and a mixed liquid outlet arranged on the mixer body; the water inlet adjustment tank (2) comprises a storage tank connected to the mixed liquid outlet, and an online pH meter arranged in the storage tank; And / or, a preheating heat exchanger (4) for exchanging heat with the outlet material of the catalytic oxidation reaction unit is further provided between the boosting pump (3) and the catalytic oxidation reaction unit; wherein the cold side of the preheating heat exchanger (4) is connected to the outlet of the boosting pump (3) and the inlet of the catalytic oxidation reaction unit, and the hot side of the preheating heat exchanger (4) is connected to the outlet of the catalytic oxidation reaction unit; optionally, the preheating heat exchanger (4) includes one of a plate heat exchanger, a shell and tube heat exchanger, and a spiral plate heat exchanger; And / or, at least the inlet of the first multiphase catalytic oxidation reactor (7) in the catalytic oxidation reaction unit is provided with a non-gaseous oxidant addition pipeline mixer (5), and the non-gaseous oxidant addition pipeline mixer (5) is provided with a non-gaseous oxidant addition port; And / or, a gaseous oxidant injection port (11) is provided at the bottom of each multiphase catalytic oxidation reactor (7) in the catalytic oxidation reaction unit.

3. The multiphase catalytic oxidation system according to claim 1 or 2, characterized in that: The catalytic oxidation reaction unit comprises 2 to 4 multiphase catalytic oxidation reactors (7) connected in series, preferably 3 multiphase catalytic oxidation reactors (7) connected in series; And / or, each multiphase catalytic oxidation reactor (7) in the catalytic oxidation reaction unit is also provided with an online thermometer and an online pressure gauge; And / or, each multiphase catalytic oxidation reactor (7) in the catalytic oxidation reaction unit is also provided with an online oxidant concentration meter.

4. The multiphase catalytic oxidation system according to any one of claims 1 to 3, characterized in that: A heater (6) is provided at the inlet of at least the first heterogeneous catalytic oxidation reactor (7) in the catalytic oxidation reaction unit; And / or, the pH callback pipeline mixer (9) is also provided with an online pH meter; And / or, a final cooling heat exchanger (8) for exchanging heat with circulating cooling water is further provided before the pH callback pipeline mixer (9); optionally, the final cooling heat exchanger (8) includes one of a plate heat exchanger, a shell and tube heat exchanger, and a spiral plate heat exchanger.

5. The multiphase catalytic oxidation system according to claim 4, characterized in that: The heater (6) is a raw water heater; And / or, a gas-liquid separator (10) is further provided after the final cooling heat exchanger (8).

6. A heterogeneous catalytic oxidation process for treating organic wastewater, characterized in that: The organic wastewater is degraded by utilizing the heterogeneous catalytic oxidation system for treating organic wastewater as described in any one of claims 1 to 5.

7. The multiphase catalytic oxidation process according to claim 6, characterized in that: The specific treatment process of the multi-phase catalytic oxidation process includes: passing the wastewater to be treated into the acid adjustment unit through the wastewater inlet pipeline to be treated, and adding acid to adjust the pH of the wastewater to be treated; the wastewater after acid adjustment is pressurized by a booster pump (3) and then flows through the catalytic oxidation reaction unit and the pH adjustment pipeline mixer (9) in sequence before being discharged.

8. The multiphase catalytic oxidation process according to claim 7, characterized in that: The wastewater pressurized by the booster pump (3) also flows through the preheating heat exchanger (4) to exchange heat with the outlet water of the catalytic oxidation reaction unit to increase the temperature; after the outlet water of the catalytic oxidation reaction unit flows through the preheating heat exchanger (4), it also flows through the final cooling heat exchanger (8) to exchange heat again and cool down; when a gaseous oxidant is used, the wastewater after the second heat exchange and cooling also flows through the gas-liquid separator (10) to separate the gas and liquid; and / or, the wastewater is subjected to non-gaseous oxidant addition or / and heating at least at the inlet of the first multi-phase catalytic oxidation reactor (7) in the catalytic oxidation reaction unit where the treatment temperature and treatment pressure decrease successively along the flow direction of the wastewater; optionally, the non-gaseous oxidant comprises hydrogen peroxide; And / or, when a gaseous oxidant is used, a gaseous oxidant injection port (11) is provided at the bottom of each multiphase catalytic oxidation reactor (7) in the catalytic oxidation reaction unit; optionally, the gaseous oxidant is an oxygen-containing gas.

9. The multiphase catalytic oxidation process according to claim 7 or 8, characterized in that: The temperature of the first multiphase catalytic oxidation reactor (7) in the flow direction of the wastewater to be treated is 160-200°C, the pressure is 0.8-1.8MPa, the temperature loss between two adjacent multiphase catalytic oxidation reactors is controlled below 20°C, and the temperature of the outlet water of the entire catalytic oxidation reaction unit is controlled above 80°C; And / or, the residence time of the first multiphase catalytic oxidation reactor (7) in the catalytic oxidation reaction unit is 10-30 min, and the total residence time of the entire catalytic oxidation reaction unit is 60-120 min.

10. The multiphase catalytic oxidation process according to any one of claims 7 to 9, characterized in that: The acid used in the acid adjustment unit includes sulfuric acid and / or hydrochloric acid; And / or, the pH of the wastewater after acid adjustment is 2-4; And / or, the lift of the booster pump (3) is set to 80-180m; And / or, the catalyst in the catalytic oxidation reaction unit includes at least one of a targeted catalyst for treating wastewater containing heterocyclic compounds, a targeted catalyst for treating wastewater containing aromatic compounds, and a targeted catalyst for treating wastewater containing hydrocarbons; And / or, the alkali used in the pH adjustment pipeline mixer (9) includes sodium hydroxide.

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