Shutdown treatment system for tail gas of formaldehyde prepared by iron-molybdenum method

Abstract

The utility model relates to the technical field of formaldehyde production, in particular to a shutdown treatment system for tail gas generated during preparation of formaldehyde by using an iron-molybdenum method. The tail gas reaction device is used for receiving and treating tail gas. The first-stage preheater is used for preheating tail gas which is pre-conveyed into the tail gas reaction device and is subjected to reaction acceleration under the auxiliary action of a catalyst, and the tail gas subjected to multiple times of circulating treatment is finally discharged from an outlet of the first-stage preheater. And the secondary preheater arranged in the cavity of the tail gas reaction device is used for tracing heat of tail gas flowing into the cavity of the shell. Thus, before formal reaction, the tail gas firstly flows into the primary preheater to be preheated for the first time, and before the tail gas flows into the tail gas reaction device to be subjected to formal reaction, the tail gas is preheated for the second time through the secondary preheater arranged in the tail gas reaction device for the second time; furthermore, part of the tail gas which is not completely reacted and is at the temperature lower than 170 DEG C can be repeatedly circulated between the first-stage preheater and the tail gas reaction device for multiple times after passing through the tail gas reaction device, so that the reaction completeness is further improved.

Description

Technical Field

[0001] The utility model relates to the technical field of formaldehyde production, in particular to a parking treatment system for formaldehyde tail gas produced by an iron-molybdenum method. Background Art

[0002] In the process of preparing formaldehyde using the iron-molybdenum process, the process tail gas contains, in addition to nitrogen, oxygen, water, carbon dioxide and other substances, a large amount of unreacted methanol, unabsorbed formaldehyde gas, side reaction products carbon monoxide, dimethyl ether and other gas phase substances. In order to avoid environmental pollution, in the prior art, the polluting gas phase substances are directly transported to the tail gas reactor R-102 for disposal (such as Figure 1 The main reactions are as follows:

[0003]

[0004] According to common sense and production experience, the gas phase temperature entering the reactor needs to be controlled above 170°C, and the reaction process can be efficient and complete, so that the non-methane total hydrocarbons and other organic substances in the tail gas can meet the emission standards. However, in actual operation, during the shutdown process of the iron-molybdenum formaldehyde equipment, the input process of raw methanol is interrupted, and in order to further reduce the concentration of combustible gas in the process gas in the iron-molybdenum formaldehyde equipment to a safe range (the indicator is that the oxygen content reaches more than 20%), the fan must be turned on for more than 20 minutes after shutdown, so that the concentration of the reactants shows a rapid downward trend, which leads to a reduction in reaction heat. In severe cases, the gas phase temperature entering the reactor is even lower than 170°C, resulting in a decrease in the reaction conversion rate, and the non-methane total hydrocarbons and other organic substances in the exhaust gas rise to the allowable emission value of more than 80mg / L, which ultimately leads to excessive exhaust gas during the shutdown process and short-term environmental pollution. Therefore, it is urgent for technical personnel to solve the above problems. Summary of the invention

[0005] Therefore, in view of the above-mentioned existing problems and defects, the designers of the present invention collected relevant information, conducted multiple evaluations and considerations, and continued to experiment and modify the system after many years of R&D experience by technicians engaged in this industry, which ultimately led to the emergence of the iron-molybdenum method formaldehyde exhaust gas parking treatment system.

[0006] In order to solve the above technical problems, the utility model relates to a system for stopping and treating tail gas from formaldehyde produced by the iron-molybdenum method, including a tail gas reaction device. The tail gas reaction device is used to receive the tail gas directly discharged by the iron-molybdenum formaldehyde preparation equipment, so that the concentration of non-methane total hydrocarbons can be reduced to below the allowable value. The tail gas reaction device includes a shell and a catalyst plate in its cavity. In addition, the system for stopping and treating tail gas from formaldehyde produced by the iron-molybdenum method also includes a primary preheater and a secondary preheater. The primary preheater is used to preheat the tail gas directly discharged by the iron-molybdenum formaldehyde preparation equipment, pre-transported to the shell cavity, and accelerated to react with the assistance of the catalyst plate. The tail gas after multiple cycles of treatment is finally discharged through its outlet. The secondary preheater is used to continuously heat the tail gas flowing into the shell cavity. It is built into the cavity of the tail gas reaction device and is located upstream of the catalyst plate.

[0007] As a further improvement of the technical solution disclosed in the utility model, the first-stage preheater is preferably a conduction heat transfer preheater or a radiation heat transfer preheater.

[0008] As a further improvement of the technical solution disclosed in the utility model, the secondary preheater is preferably an electric heating type preheater, which includes a mounting seat, an electric heating rod and an electric insulation shell. The mounting seat is used to plug and fix the electric heating rod, and it is detachably and horizontally fixed on the inner side wall of the shell. The electric insulation shell uses the mounting seat as an assembly basis, and it forms circumferential electric insulation protection for the electric heating rod.

[0009] As a further improvement of the technical solution disclosed in the utility model, the electrical insulating shell is preferably made of alumina ceramics, magnesium oxide ceramics or graphene.

[0010] As a further improvement of the technical solution disclosed in the utility model, the tail gas reaction device also includes a gas distribution plate. The gas distribution plate is horizontally placed in the cavity of the shell and is located downstream of the secondary preheater and upstream of the catalyst plate.

[0011] In practical applications, the iron-molybdenum method formaldehyde tail gas parking treatment system disclosed in the utility model has achieved at least the following beneficial technical effects, specifically:

[0012] 1) Before entering the tail gas reaction device for formal reaction, the tail gas discharged from the iron-molybdenum formaldehyde preparation equipment first flows into the primary preheater for preheating (design temperature 150-155°C), and then flows into the tail gas reaction device. Before the formal reaction, it is preheated twice by the secondary preheater built in the tail gas reaction device, and the tail gas temperature finally reaches 170°C, ensuring that the subsequent catalytic reaction process can be carried out efficiently and completely;

[0013] 2) After passing through the tail gas reaction device, some of the tail gas that has not been completely reacted and has a temperature below 170°C can be repeatedly circulated between the primary preheater and the tail gas reaction device for multiple times, and the completeness of the reaction can be further improved until the non-methane total hydrocarbons and other organic substances in the tail gas meet the emission standards. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0015] Figure 1 It is a structural schematic diagram of a formaldehyde tail gas parking treatment system using the iron-molybdenum method in the prior art.

[0016] Figure 2 The utility model discloses a structural schematic diagram of a formaldehyde tail gas parking treatment system using an iron-molybdenum method.

[0017] Figure 3 The utility model discloses a schematic diagram of the structure of a secondary preheater in a parking treatment system for formaldehyde tail gas produced by an iron-molybdenum method.

[0018] 1- tail gas reaction device; 11- shell; 12- catalyst plate; 13- gas distribution plate; 2- primary preheater; 3- secondary preheater; 31- mounting seat; 32- electric heating rod; 33- electric insulation shell. DETAILED DESCRIPTION

[0019] In the description of the present invention, it should be understood that the terms "front", "rear", "up", "down", "left", "right", etc., indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0020] The following is a further detailed description of the contents disclosed in the present utility model in conjunction with specific embodiments. Figure 2 The schematic diagram of the structure of the iron-molybdenum formaldehyde tail gas shutdown treatment system disclosed in the utility model is shown. It can be seen that it is mainly composed of a tail gas reaction device 1, a primary preheater 2 and a secondary preheater 3. Among them, the tail gas reaction device 1 is used to receive the tail gas directly discharged by the iron-molybdenum formaldehyde preparation equipment to reduce the concentration of non-methane total hydrocarbons to below the allowable value. Figure 3As shown in the figure, the exhaust gas reaction device 1 includes a shell 11 and a catalyst plate 12 in its cavity. The primary preheater 2 is arranged upstream of the exhaust gas reaction device 1, and is used to preheat the exhaust gas directly discharged from the iron-molybdenum formaldehyde preparation device, pre-transported to the cavity of the shell 11, and accelerated with the assistance of the catalyst plate 12. The exhaust gas after multiple cycles is finally discharged through its outlet. The secondary preheater 3 is used to continuously heat the exhaust gas flowing into the cavity of the shell 11. It is built into the cavity of the exhaust gas reaction device 1 and is located upstream of the catalyst plate 12.

[0021] In practical applications, the iron-molybdenum formaldehyde tail gas shutdown treatment system disclosed in the utility model has achieved at least the following beneficial technical effects. On the one hand, before entering the tail gas reaction device 1 for formal reaction, the tail gas discharged by the iron-molybdenum formaldehyde preparation equipment first flows into the primary preheater 2 for preheating (design temperature 150-155°C), and then flows to the tail gas reaction device 1, and before the formal reaction, it is preheated for the second time through the secondary preheater 3 arranged in the tail gas reaction device 1, and the tail gas temperature finally reaches 170°C, ensuring that the subsequent catalytic reaction process can be carried out efficiently and completely; on the other hand, after passing through the tail gas reaction device, some of the tail gas that has not been completely reacted and has a temperature below 170°C can be repeatedly circulated between the primary preheater 2 and the tail gas reaction device 1 for multiple times, and the completeness of the reaction can be further improved until the non-methane total hydrocarbons and other organic substances in the tail gas meet the emission standards.

[0022] Preheaters are usually used in the heat exchange process in industrial production, and are divided into conduction, convection and radiation according to different heat transfer methods. At the beginning of the project, the first-stage preheater 2 was selected as a conduction heat transfer preheater, and it was mainly achieved through heat conduction. The heat was transferred from the high-temperature area to the low-temperature area to increase the temperature of the exhaust gas to be heated. The heat transfer parts of the conduction heat transfer preheater are made of high thermal conductivity metal materials, usually copper or aluminum. The conduction heat transfer preheater achieved the expected effect, but its design structure is relatively complex and the procurement cost is relatively high. In view of this, the second phase project selected the first-stage preheater 2 as a radiation heat transfer preheater, which transfers heat through electromagnetic waves during the working process, thereby effectively expanding the heating range, and the copper and aluminum heating plates with good heat conductivity and high purchase cost were eliminated in the structural design.

[0023] Furthermore, by Figure 3As shown in the figure, it can be clearly seen that in this embodiment, the secondary preheater 3 is preferably an electric heating type preheater, and it is mainly composed of several parts such as a mounting seat 31, an electric heating rod 32 and an electric insulating shell 33. The mounting seat 31 is used to plug and fix the electric heating rod 32, and it is detachably and horizontally fixed on the inner wall of the shell 11. The electric insulating shell 33 uses the mounting seat 31 as the assembly basis, and it forms a circumferential electrical insulation protection for the electric heating rod 32. And the electric insulating shell 33 is preferably made of alumina ceramic, magnesium oxide ceramic or graphene. In the exhaust gas treatment process, the exhaust gas heated by the primary preheater 1 continues to flow into the cavity of the exhaust gas reaction device 1. Before the catalytic reaction is formally accelerated, the electric heating rod 32 continuously emits heat with the assistance of electricity, and adopts a thermal radiation method to perform a secondary temperature treatment on the exhaust gas within the range until the gas phase temperature reaches 170°C, ensuring that the catalytic reaction process can be carried out efficiently and completely, thereby ensuring that the non-methane total hydrocarbons and other organic substances in the exhaust gas pre-discharged into the atmosphere meet the emission standards.

[0024] Under the premise that the exhaust gas flowing into the cavity of the exhaust gas reaction device 1 is effectively heated, in order to ensure that the exhaust gas after the gas phase temperature reaches the standard has a larger contact area with the catalyst plate 12, thereby facilitating the catalytic reaction efficiency and reaction completeness to be effectively improved, in view of this, as a further optimization of the above technical solution, a gas distribution plate 13 is further provided inside the exhaust gas reaction device 1. The gas distribution plate 13 is horizontally placed in the cavity of the shell 11, and is located downstream of the secondary preheater 3 and upstream of the catalyst plate 12.

[0025] Finally, it should be noted that in order to further improve the catalytic reaction efficiency and completeness of the exhaust gas, in this embodiment, the catalyst plate 12 is also modified and designed. Specifically, the catalyst plate 12 is preferably a corrugated plate or a honeycomb plate (not shown in the figure), so that the catalyst has a larger specific surface area relative to the exhaust gas to be treated, which is conducive to improving the catalytic efficiency.

[0026] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A system for treating tail gas from an iron-molybdenum formaldehyde production plant, comprising a tail gas reaction device; the tail gas reaction device is used to receive tail gas directly discharged from an iron-molybdenum formaldehyde production plant, so that the concentration of non-methane total hydrocarbons can be reduced to below the allowable value; the tail gas reaction device comprises a shell and a catalyst plate in its cavity, characterized in that: It also includes a primary preheater and a secondary preheater; the primary preheater is used to preheat the tail gas directly discharged from the iron-molybdenum formaldehyde preparation device, pre-transported to the shell cavity, and accelerated to react with the assistance of the catalyst plate, and the tail gas after multiple cycles of treatment is finally discharged through its outlet; The secondary preheater is used to continuously heat the exhaust gas flowing into the shell cavity. The secondary preheater is built into the cavity of the exhaust gas reaction device and is located upstream of the catalyst plate.

2. The iron-molybdenum method formaldehyde tail gas parking treatment system according to claim 1 is characterized in that: The primary preheater is a conduction heat transfer type preheater or a radiation heat transfer type preheater.

3. The formaldehyde tail gas parking treatment system according to claim 1 is characterized in that: The secondary preheater is an electric heating type preheater, which includes a mounting seat, an electric heating rod and an electric insulating shell; the mounting seat is used to plug and fix the electric heating rod, and it is detachably and horizontally fixed on the inner wall of the shell; the electric insulating shell uses the mounting seat as an assembly basis, and forms circumferential electrical insulation protection for the electric heating rod.

4. The formaldehyde tail gas parking treatment system according to claim 3 is characterized in that: The electrical insulation shell is made of alumina ceramics, magnesium oxide ceramics or graphene.

5. The system for treating formaldehyde tail gas produced by the iron-molybdenum method according to any one of claims 1 to 4, characterized in that: The tail gas reaction device also includes a gas distribution plate; the gas distribution plate is horizontally placed in the cavity of the shell, and is located downstream of the secondary preheater and upstream of the catalyst plate.

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