Chlorinated flue gas waste heat recovery process

Abstract

The invention discloses a chlorinated flue gas waste heat recovery process, which relates to the field of chlorinated flue gas treatment, and sequentially comprises the following steps: (1) pretreating chlorinated flue gas from a titanium tetrachloride production process to remove most of titanium tetrachloride; (2) cooling and washing; (3) deoxidizing treatment; (4) catalytic combustion treatment; and (5) waste heat recovery. Wherein the step (1) sequentially comprises the following sub-steps: washing with chilled water, condensing and cooling; carrying out first gas-liquid separation; spraying with water; alkali spraying is performed; carrying out secondary gas-liquid separation; a system bypass and an electric valve are arranged on a pipeline between the step (1) and the step (2); a one-way anti-explosion valve is arranged on a pipeline between the step (2) and the step (3); in the step (5), a waste heat boiler with a steam pocket communicated with the waste heat boiler is used. According to the process, heat of the chlorinated flue gas can be fully recycled, and comprehensive utilization of the chlorinated flue gas is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of chlorination flue gas treatment, in particular to a chlorination flue gas pollution emission reduction and waste heat recovery process. BACKGROUND

[0002] The flue gas in the production process of titanium tetrachloride includes titanium tetrachloride (vapor), chlorine (a small amount), carbon monoxide, sulfur dioxide, greenhouse gas CO2, in addition to hydrogen chloride, oxygen and nitrogen. These flue gases will still contain low concentrations of carbon monoxide after being treated by traditional technology, causing air pollution. Due to the presence of a large amount of N2 and CO2 in the flue gas and the low concentration of carbon monoxide, the chlorination flue gas containing carbon monoxide has low calorific value, is difficult to ignite, and has poor combustion performance, etc. In the prior art, the chlorination flue gas is discharged after simple treatment (such as water washing condensation, gas-liquid separation), which not only pollutes the atmosphere, but also cannot effectively recover and utilize the heat of the chlorination flue gas.

[0003] Therefore, it is necessary to develop a chlorination flue gas pollution emission reduction and waste heat recovery process to effectively utilize heat energy and reduce pollution emissions. SUMMARY

[0004] The purpose of the present application is to provide a chlorination flue gas waste heat recovery process, which can effectively recover waste heat and realize the comprehensive utilization of the heat energy of chlorination flue gas.

[0005] Therefore, the present application provides a chlorination flue gas waste heat recovery process, which comprises the following steps in sequence: (a) pre-treating the chlorination flue gas from the production process of titanium tetrachloride in a pre-treatment subsystem to remove most of the titanium tetrachloride; (b) cooling and washing the chlorination flue gas in a cooling and washing device; (c) removing oxygen from the chlorination flue gas in an oxygen removal device; (d) catalytically combusting the chlorination flue gas in a catalytic combustion subsystem; and (e) recovering waste heat in a waste heat recovery subsystem; wherein the pre-treatment in step (a) comprises the following sub-steps in sequence: water washing condensation cooling with chilled water to precipitate titanium tetrachloride droplets; first gas-liquid separation with a first gas-liquid separator to separate out the droplets and solid impurities; water spraying with a water spraying device to generate hydrochloric acid from chlorine in the flue gas; alkali spraying with an alkali spraying device to neutralize the hydrochloric acid and remove hydrochloric acid droplets and sulfides; second gas-liquid separation with a second gas-liquid separator to further condense the droplets from the spraying device and collect them again; a system bypass and an electric valve are provided on the pipeline between step (a) and step (b); a one-way explosion-proof valve is provided on the pipeline between step (b) and step (c); step (e) uses a waste heat boiler with a steam drum connected thereto, and the waste heat boiler heats feed water using the heat of the flue gas and delivers steam to the outside from the steam drum.

[0006] Further, a flue gas preheater is arranged on the pipeline between the one-way explosion-proof valve and step (c), which uses a small amount of flue gas from step (e) to preheat the main flue gas to be introduced into step (c), and the chlorinated flue gas with reduced temperature after passing through the flue gas preheater is recycled to step (e) or discharged into a chimney. When the flue gas preheater is used, most of the chlorinated flue gas from the waste heat boiler enters the downstream process, and a small amount of the chlorinated flue gas is recycled to the flue gas preheater for further use of the waste heat of the chlorinated flue gas.

[0007] Further, the chlorinated flue gas from step (a) is introduced into step (b) through a pressure detection instrument and a booster fan. In step (b), heat exchange and temperature reduction (condensation and moisture removal) are performed by a temperature reduction washing device. The temperature reduction washing device uses water as a medium to wash and exchange heat with the flue gas to reduce the temperature of the flue gas. The water medium with increased temperature due to heat exchange can be cooled by an additional heat exchange device and then recycled to the temperature reduction washing device.

[0008] Further, the oxygen removal in step (c) is adsorption oxygen removal, and the adsorbent used is a porous material, preferably tetracyanoquinodimethane.

[0009] Further, the catalytic combustion in step (d) is performed in a catalytic combustion barrel containing honeycomb-shaped ceramics as heat accumulators inside. Further, the catalyst in step (d) uses honeycomb-shaped ceramics as a carrier, and the carrier is coated with an active component, which is a noble metal or a transition metal oxide.

[0010] Further, step (d) is assisted by supplemental natural gas combustion.

[0011] Further, the oxygen removal device is a catalytic oxygen removal device capable of causing carbon monoxide to undergo an oxidation reaction at a temperature of 150-300 degrees Celsius.

[0012] Further, the catalyst used by the catalytic oxygen removal device is a catalyst using honeycomb-shaped ceramics as a carrier and platinum metal as an active component. The honeycomb-shaped ceramics are preferably cordierite.

[0013] The present application can achieve the following beneficial effects: The flue gas treatment system and process of the present application can effectively reduce pollution emissions, and can safely and fully recover waste heat of chlorination flue gas, realizing safe and efficient comprehensive utilization of chlorination flue gas. The present application recovers and utilizes heat generated by combustion in the catalytic combustion subsystem through the waste heat recovery subsystem, most of the heat is used to generate steam and the steam is delivered outward through the steam drum, thereby realizing the purpose of waste heat recovery and utilization, and the remaining heat is further recovered and utilized through the flue gas preheater, the air preheater and the feed water preheater, thereby greatly improving the comprehensive utilization rate. At the same time, through the combustion of low-calorific-value carbon monoxide, the concentration of low-concentration carbon monoxide is reduced again, thereby greatly reducing the pollution to the atmosphere.

[0014] In addition, in some embodiments of the present application, in addition to producing steam by the waste heat boiler, the heat of the flue gas from the waste heat recovery subsystem is comprehensively utilized through various ways, thereby greatly improving the recovery and utilization efficiency. Among them, the flue gas preheater can utilize the heat of a small part of the flue gas to preheat the main flue gas, and the remaining most of the flue gas can preheat fresh air to be introduced into the catalytic combustion subsystem through the air preheater and preheat desalted water to be introduced into the steam drum through the feed water preheater. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a schematic diagram of the connection relationship of each part in the overall structure of the flue gas waste heat recovery system of the present application; Figure 2 is a schematic diagram of the chlorination flue gas waste heat recovery process of the present application; Figure 3 is a schematic diagram of a more specific process of the chlorination flue gas waste heat recovery process of the present application; In the figure: 1, pretreatment subsystem; 101, first gas-liquid separator; 102, spraying device; 1021, water spraying device; 1022, alkali spraying device; 103, second gas-liquid separator; 104, induced draft fan; 105, main road electric valve; 106, system bypass electric valve; 107, booster fan; 2, cooling and washing device; 201, heat exchanger; 202, refrigerated brine system; 203, heat exchanger circulating pump; 3, deaerating device; 4, catalytic combustion subsystem; 5, waste heat recovery subsystem; 501, waste heat boiler; 502, steam drum; 503, feed water preheater; 504, dust collector; 505, feed water pump; 506, air blower; 507, fan; 508, air preheater; 6, chimney; 7, flue gas preheater; 8, one-way explosion-proof valve. DETAILED DESCRIPTION

[0016] Unless otherwise specified, the "content" of a gas in the present application refers to the volume percentage content.

[0017] The present application will be described in more detail below.

[0018] As mentioned above, the present application provides a chlorination flue gas waste heat recovery process, which comprises the following steps in sequence: (a) pre-treating the chlorination flue gas from a titanium tetrachloride production process in a pre-treatment subsystem to remove most of the titanium tetrachloride; (b) cooling and washing the chlorination flue gas in a cooling and washing device; (c) removing oxygen from the chlorination flue gas in an oxygen removal device; (d) catalytically combusting the chlorination flue gas in a catalytic combustion subsystem; and (e) recovering waste heat in a waste heat recovery subsystem; wherein the pre-treatment in step (a) comprises the following sub-steps in sequence: condensing and cooling with chilled water to precipitate titanium tetrachloride droplets; performing first gas-liquid separation with a first gas-liquid separator to separate out the droplets and solid impurities; spraying water (preferably multi-stage spraying, such as three-stage spraying) with a water spraying device to generate hydrochloric acid from chlorine in the flue gas; spraying alkali (preferably multi-stage spraying, such as two-stage spraying) with an alkali spraying device to neutralize the hydrochloric acid and remove hydrochloric acid droplets and sulfides; performing second gas-liquid separation with a second gas-liquid separator to further condense and collect the droplets from the spraying device; providing a system bypass and an electric valve on the pipeline between step (a) and step (b); providing a one-way explosion-proof valve on the pipeline between step (b) and step (c); and using a waste heat boiler with a steam drum connected thereto in step (e), the waste heat boiler heating feed water using the heat of the flue gas and delivering steam from the steam drum.

[0019] The system bypass can be used to shut down the process when necessary (e.g. in an emergency) to allow the chlorination flue gas to be discharged directly from the chimney without entering the cooling and washing device. Further, an induced draft fan, a main route electric valve, a pressure detection instrument, and a booster fan are provided in sequence on the flue gas pipeline of the pre-treatment and the cooling and washing process, a system bypass is provided between the induced draft fan and the main route electric valve, the system bypass is connected to the chimney, a system bypass electric valve is provided in the system bypass, the pressure detection instrument is used to detect the flue gas pressure in the main route, the booster fan is used to increase the flue gas pressure to form a high-speed airflow in the cyclone inside the cooling and washing device, and the system bypass electric valve is used to open the system bypass to allow the flue gas to be discharged directly from the chimney when necessary, and the main route electric valve is linked to the system bypass electric valve to shut down the main route when the system bypass is started.

[0020] The one-way explosion-proof valve can be used to prevent the cooling and washing device and the system upstream thereof from exploding due to backfire, so that the process can be reliably shut down in the event of an accidental explosion to avoid affecting the operation of the main production system.

[0021] A flue gas preheater can be provided on the pipeline between the one-way explosion-proof valve and step (c), which preheats the main flue gas to be introduced into step (c) by using a small amount of flue gas from step (e), and the chlorinated flue gas with reduced temperature after passing through the flue gas preheater is recycled to step (e) or discharged into a chimney. When the flue gas preheater is used, most of the chlorinated flue gas from the waste heat boiler enters the downstream process, and a small amount of it is recycled to the flue gas preheater for further use of the waste heat of the chlorinated flue gas.

[0022] The chlorinated flue gas from step (a) can be introduced into step (b) through a pressure detection instrument and a booster fan. In step (b), heat exchange and cooling (condensation and dehumidification) are carried out by a cooling and washing device. The cooling and washing device uses water as a medium to wash and exchange heat with the flue gas to reduce the temperature of the flue gas. The water medium with increased temperature due to heat exchange can be cooled by an additional heat exchange device and then recycled to the cooling and washing device.

[0023] The present application does not have special restrictions on the cooling and washing device. Preferably, the cooling and washing device comprises a device with a fire blocking function, more preferably a cyclone water seal fire blocking device. Further, the cooling and washing device comprises: a cooling and washing device body which uses water inside to cool and wash the flue gas from the pretreatment subsystem; a heat exchanger (such as a condenser, for example, a GGH condenser) which communicates with the cooling and washing device body through an inlet water pipe and an outlet water pipe, for cooling the water from the cooling and washing device body and entering the heat exchanger through the inlet water pipe by heat exchange, and recycling the water into the cooling and washing device body through the outlet water pipe; and a refrigerated brine system which communicates with the heat exchanger through an outlet brine pipe and an inlet brine pipe, refrigerated brine from the refrigerated brine system enters the heat exchanger through the outlet brine pipe for heat exchange, and then is recycled into the refrigerated brine system through the inlet brine pipe, the refrigerated brine system uses the refrigerated brine to cool the water from the cooling and washing device body in the heat exchanger.

[0024] The present invention does not impose any particular limitations on the deoxygenation device. However, according to certain embodiments, the deoxygenation device is an adsorption deoxygenation device that utilizes a porous adsorption material (e.g., tetracyanoquinodimethane) to adsorb oxygen and / or a catalytic deoxygenation device that utilizes a catalyst to catalyze the oxygen reaction, preferably a catalytic deoxygenation device. Preferably, the catalytic deoxygenation device is a catalytic deoxygenation device capable of catalytic deoxygenation at low temperatures of 150-300 degrees Celsius, at which temperature the carbon monoxide in the flue gas undergoes an oxidation reaction with oxygen. More preferably, the catalyst used in the catalytic deoxygenation device is a precious metal catalyst coated on a honeycomb-shaped ceramic (preferably cordierite), with a platinum metal catalyst being particularly preferred. Furthermore, the amount of the platinum metal catalyst is controlled to enable the carbon monoxide to undergo an oxidation reaction at low temperatures of 150-300 degrees Celsius and to reduce the oxygen content in the flue gas to below 1 vol%. This ingenious design of the present invention prevents backfire from downstream from igniting upstream, thus avoiding catastrophic explosion accidents.

[0025] The present invention has no particular limitation on the catalytic combustion subsystem. Preferably, the catalytic combustion subsystem includes: a catalytic combustion barrel configured to combust carbon monoxide in the flue gas from the deoxygenator to produce carbon dioxide, thereby releasing heat from the flue gas. The catalytic combustion barrel further comprises a catalytic combustion barrel body, an active component, and a heat storage element. The flue gas from the deoxygenator enters the catalytic combustion barrel body through a flue gas inlet, undergoes combustion, and then enters the waste heat recovery subsystem through a flue gas outlet. The active component is disposed within the catalytic combustion barrel body and is configured to catalyze a combustion reaction (preferably flameless combustion) between carbon monoxide and oxygen in the flue gas from the deoxygenator. The heat storage element is configured to store heat and maintain it at a temperature suitable for the combustion reaction of the carbon monoxide. an air supply line for introducing fresh air into the interior of the catalytic combustion barrel through the air inlet of the catalytic combustion barrel to provide oxygen for the reaction; and The natural gas supply pipeline introduces natural gas into the catalytic combustion barrel body through the natural gas inlet of the catalytic combustion barrel body for initial ignition or for supplementary combustion when the carbon monoxide content in the flue gas is too low and the combustion is interrupted.

[0026] Preferably, the heat accumulator is a honeycomb ceramic that maintains a temperature above 600°C by accumulating heat. More preferably, the heat accumulator is loaded with the active component for catalytic combustion. The active component for catalytic combustion is preferably a precious metal, more preferably platinum. The amount of the active component for catalytic combustion is controlled within a range that allows for complete combustion (preferably flameless combustion) of carbon monoxide in the flue gas and oxygen in the air within a temperature range of 600 to 800°C.

[0027] According to some embodiments, in order to facilitate emergency treatment and ensure safety, the waste heat recovery system of the present application further comprises a system bypass located downstream of the pre-treatment subsystem and upstream of the quenching scrubber. In case of emergency or maintenance of the main system, the process can be shut down and the flue gas is not sent to the quenching scrubber but directly discharged from the chimney.

[0028] According to some embodiments, in order to further ensure safety, the waste heat recovery system of the present application further comprises a one-way explosion-proof valve arranged on the flue gas outlet pipeline of the quenching scrubber. The one-way explosion-proof valve can be used to prevent the quenching scrubber and the system upstream thereof from exploding due to backfire, so that in case of accidental explosion, the process can be reliably shut down to avoid the impact of the accident on the operation of the titanium tetrachloride main production system.

[0029] According to some embodiments, in order to raise the chlorinated flue gas entering the deoxidizing device to a suitable temperature for subsequent processing, the waste heat recovery system of the present application further comprises a flue gas preheater located downstream of the quenching scrubber and upstream of the deoxidizing device and communicating therewith. When a one-way explosion-proof valve is arranged, the flue gas preheater is arranged between the one-way explosion-proof valve and the deoxidizing device.

[0030] The waste heat recovery subsystem suitable for use in the waste heat recovery system of the present application is not particularly limited.

[0031] According to some embodiments, the waste heat recovery subsystem suitable for use in the waste heat recovery system of the present application comprises a waste heat boiler. When the waste heat recovery system of the present application employs a flue gas preheater, the chlorinated flue gas from the waste heat boiler is mostly sent to the downstream device, and a small part is circulated into the flue gas preheater for further utilization of the waste heat of the chlorinated flue gas. Further, the waste heat recovery subsystem further comprises a steam drum communicating with the waste heat boiler, and steam is delivered outward from the steam drum, thereby achieving recovery and utilization of heat energy.

[0032] According to some embodiments, in order to further improve the waste heat recovery efficiency, the waste heat recovery system of the present application further comprises: an air preheater located downstream of the waste heat recovery subsystem for preheating air using the heat from the flue gas of the waste heat recovery subsystem and feeding the preheated air into the catalytic combustion subsystem; and / or a feedwater preheater located downstream of the waste heat recovery subsystem for preheating demineralized water using the heat from the flue gas of the waste heat recovery subsystem and feeding the preheated demineralized water into the waste heat recovery subsystem. Further, the system comprises both the air preheater and the feedwater preheater. Still further, the feedwater preheater is located downstream of the air preheater. When the waste heat recovery subsystem applicable to the present application comprises a waste heat boiler and a steam drum in communication with the waste heat boiler, the demineralized water from the feedwater preheater is fed into the steam drum, which converts the demineralized water into steam for external delivery. The high-temperature flue gas after combustion in the catalytic combustion barrel is discharged into the waste heat boiler through a plurality of flue gas discharge pipes, for example, two flue gas discharge pipes. The waste heat boiler has a plurality of serpentine heat exchange pipes therein, and water from the steam drum flows in the heat exchange pipes. The heat exchange pipes are heated by the high-temperature flue gas to convert the demineralized water into water vapor, which is evaporated into the steam drum and externally delivered through an upper pipeline for power generation or work. The external delivery of the steam reduces the water level in the steam drum, and the demineralized water from the feedwater preheater continues to supplement the water in the steam drum.

[0033] According to some particularly preferred embodiments of the present application, the system comprises the pretreatment subsystem as described above, and a flue gas duct is sequentially connected between the pretreatment subsystem and the cooling and washing device. A primary air fan, a primary air electric valve, a pressure detection instrument and a booster fan are sequentially connected in the flue gas duct. A system bypass is provided between the primary air fan and the primary air electric valve, and the system bypass is connected to a chimney. A system bypass electric valve is provided in the system bypass. The pressure detection instrument is used to detect the pressure of the flue gas in the primary air. The booster fan is used to increase the pressure of the flue gas to form a high-speed airflow in the cyclone inside the cooling and washing device. The system bypass electric valve is used to open the system bypass to directly discharge the flue gas from the chimney when needed. The primary air electric valve is linked with the system bypass electric valve to cut off the primary air when the system bypass is started.

[0034] A one-way explosion-proof valve and a flue gas preheater are sequentially connected in the flue gas duct between the cooling and washing device and the deaerating device. The one-way explosion-proof valve is used to prevent explosion caused by backfire from the catalytic combustion subsystem. The flue gas preheater is used to preheat the flue gas from the one-way explosion-proof valve and send it into the deaerating device.

[0035] The oxygen removal device is a catalytic oxygen removal device capable of catalytic oxygen removal at a low temperature of 150-300 degrees Celsius, and the catalyst used by the catalytic oxygen removal device is a catalyst using honeycomb cordierite as a carrier and platinum metal as an active component, and the amount of the platinum metal is controlled to enable carbon monoxide to undergo an oxidation reaction at a low temperature of 150-300 degrees Celsius and to reduce the oxygen content in the flue gas to below 1 vol%.

[0036] The catalytic combustion subsystem comprises: a catalytic combustion barrel for burning carbon monoxide in the flue gas from the oxygen removal device to generate carbon dioxide to release the heat of the flue gas, the catalytic combustion barrel further comprising: a catalytic combustion barrel body, the flue gas from the oxygen removal device enters the inside of the catalytic combustion barrel body through a flue gas inlet and is sent into the waste heat recovery subsystem through a flue gas outlet after combustion; an active component arranged inside the catalytic combustion barrel body for catalyzing the combustion reaction between carbon monoxide in the flue gas from the oxygen removal device and oxygen, and the amount of the active component is controlled to enable carbon monoxide in the flue gas and oxygen in the air to fully combust within a temperature range of 600 to 800 degrees Celsius; and a heat accumulator which is a honeycomb ceramic and loads the active component as a carrier, and is capable of maintaining the temperature in the range of 600 to 800 degrees Celsius by accumulating heat; an air supply pipeline for supplying fresh air into the inside of the catalytic combustion barrel through an air inlet of the catalytic combustion barrel to provide oxygen for combustion; and a natural gas supply pipeline for supplying natural gas for supplementary combustion into the inside of the catalytic combustion barrel body through a natural gas inlet of the catalytic combustion barrel to deal with the situation of insufficient carbon monoxide content in the flue gas during system startup and operation; The waste heat recovery subsystem comprises: a waste heat boiler and a steam drum connected to the inside of the waste heat boiler, wherein the steam drum is used to receive feed water and to continuously send out steam, the feed water in the steam drum enters the heat exchange serpentine pipes in the inside of the waste heat boiler body, exchanges heat with the high-temperature flue gas from the catalytic combustion subsystem outside the pipes, and then circulates to the steam drum, the steam drum continuously sends out steam to realize waste heat recovery, and the water supplemented according to the steam delivery amount continuously supplies the steam drum through a feed water outlet pipeline; an air preheater located downstream of the waste heat boiler, for preheating air using the residual heat of the flue gas from the waste heat boiler and feeding the preheated air into the catalytic combustion subsystem; a feed water preheater located downstream of the air preheater, for preheating desalted water using the residual heat of the flue gas from the air preheater and feeding the preheated desalted water into the steam drum; and A flue gas circulation branch is arranged between the waste heat boiler and the flue gas preheater, and is used to send a part of the flue gas from the waste heat boiler into the flue gas preheater and circulate to the waste heat boiler, and the flue gas preheater is preheated by the heat of the part of the flue gas from the upstream flue gas, and the preheated flue gas enters the oxygen removal device, while the flue gas in the flue gas circulation branch is circulated into the waste heat boiler, and the flue gas circulation branch is provided with a valve on the pipeline before the circulating flue gas enters the flue gas preheater to open and close the flue gas circulation branch when needed, and the flue gas circulation branch is provided with a fan on the pipeline after the circulating flue gas leaves the flue gas preheater to send the circulating flue gas into the waste heat boiler; The catalytic combustion barrel is arranged next to the waste heat boiler and sends the flue gas into the waste heat boiler through a plurality of flue gas outlet pipes, so that the flue gas is sent into the waste heat boiler as soon as possible. The flue gas from the feed water preheater is sent into the chimney after being dedusted by the dust remover, and a flue gas detection device is installed at the chimney outlet to ensure that the flue gas meets the relevant emission standards and to monitor the system processing effect.

[0037] The components of the present application are described one by one as follows.

[0038] Pretreatment subsystem The present application does not have special restrictions on the pretreatment subsystem, and any device capable of pretreating flue gas, especially chlorinated flue gas, can be used in the waste heat recovery system of the present application. Those devices in the prior art that treat chlorinated flue gas before it is discharged can be used as the pretreatment subsystem of the waste heat recovery system of the present application.

[0039] For example, the pretreatment subsystem can include, in sequence, a first gas-liquid separator for gas-liquid separation of the flue gas, a spraying device downstream of the gas-liquid separator for spraying treatment of the flue gas, and a second gas-liquid separator downstream of the spraying device for re-gas-liquid separation of the flue gas. Further, the spraying device includes, in sequence, a water spraying device and an alkali spraying device. Both the water spraying device and the alkali spraying device are preferably composed of multiple levels of spraying devices connected in series. The chlorinated flue gas is sprayed with water to obtain by-product hydrochloric acid (chlorine reacts with water to obtain hydrochloric acid), and is sprayed with alkali (for example, with sodium hydroxide solution) to remove hydrochloric acid droplets and sulfides. Further, a water washing condensing device is arranged upstream of the first gas-liquid separator, which uses chilled water to wash and condense the chlorinated flue gas to precipitate titanium tetrachloride droplets. The first gas-liquid separator separates the titanium tetrachloride droplets in the chlorinated flue gas, and the remaining chlorinated flue gas mainly includes chlorine, carbon monoxide and other flue gases, and a small amount of titanium tetrachloride, and the temperature of the chlorinated flue gas is also significantly reduced (for example, to about minus ten degrees Celsius). The second gas-liquid separator can further condense and collect the droplets from the spraying device.

[0040] It should be understood that the chlorination flue gas from the titanium tetrachloride production process can also, in some cases (e.g. lower impurity content), be directly fed into the quenching scrubber without the pretreatment subsystem for quenching scrubbing treatment. However, preferably, the waste heat recovery system of the present application comprises a pretreatment subsystem.

[0041] System bypass A system bypass is not necessary for the waste heat recovery system of the present application. However, in order to ensure the safety of the titanium tetrachloride main production system, and to facilitate emergency disposal, the waste heat recovery system of the present application preferably comprises a system bypass, which is preferably located downstream of the pretreatment subsystem and upstream of the quenching scrubber. An electrically operated valve can be provided in the system bypass, which can be opened to shut off the process and let the chlorination flue gas directly discharged from the chimney when necessary (e.g. in an emergency).

[0042] Quenching scrubber The quenching scrubber of the present application is not particularly limited, and any device capable of quenching scrubbing of the chlorination flue gas can be used in the waste heat recovery system of the present application. A quenching scrubber with a fire-retardant function is preferred. For example, the quenching scrubber can comprise a quenching scrubber and a fire-retardant device respectively, or a quenching scrubber with both quenching and fire-retardant functions can be used, such as a quenching scrubber with an internal cyclone with static vanes to form a cyclone water seal to achieve the fire-retardant function.

[0043] According to some embodiments, the quenching scrubber is provided with a heat exchanger (preferably a GGH condenser, i.e. a condenser device associated with a "Gas Gas Heater") in communication with the main body of the quenching scrubber, for heat exchange between the water medium from the bottom of the quenching scrubber and the chilled brine from the chilled brine system to achieve quenching (e.g. from 40°C to 20°C, and correspondingly the chilled brine can be raised from 0°C to 20°C), and then circulated into the main body of the quenching scrubber. In this case, the heat exchanger is used as a liquid storage mechanism, and there can be multiple liquid storage mechanisms, for example two. As an alternative, the quenching scrubber can directly use the circulating chilled brine for washing, which is drawn from the liquid storage mechanism into the quenching scrubber and then circulated into the liquid storage mechanism. As another alternative, the quenching scrubber can also use the original flue gas (about minus 10°C to 0°C) from the titanium tetrachloride production process to quench the circulating water (e.g. about 40°C) from the bottom of the quenching scrubber by providing a cooling tower. The heat-exchanged original chlorination flue gas is introduced into the quenching scrubber 2. The outlet temperature of the heat-exchanged original chlorination flue gas and the temperature of the circulating water medium can be controlled at the same lower temperature, for example both at 20°C.

[0044] The cyclone of the present application is not particularly limited, and any device capable of forming a cyclone can be used in the present application. However, preferably, the cyclone is an emulsion layer cyclone. The emulsion layer cyclone refers to a cyclone that can form an emulsion layer inside the cyclone. More preferably, the cyclone comprises at least one (preferably at least two, more preferably two) cyclone vane module (such as a static vane that can be passively rotated under the action of fluid). It is particularly preferred that the cyclone vane module comprises a sleeve and a plurality of static vanes, which are preferably arranged obliquely. By arranging the static vanes obliquely, the flue gas flow can be caused to undergo strong planar centripetal rotation when passing through the static vanes of the cyclone vane module, and the rotating flue gas impacts the liquid into a rotating foam zone, and then lifts up the foam zone, so that the entire rotating foam zone is in a suspended state, and the flue gas passes through the foam zone and the rotating downward liquid from bottom to top for sufficient action, achieving the purpose of cooling and washing the chlorinated flue gas, and at the same time, the water seal formed by the cyclone vane module achieves the purpose of effective fireproofing.

[0045] The one-way explosion-proof valve is not necessary for the waste heat recovery system of the present application. However, in order to further ensure safety, especially the safety of the titanium tetrachloride main production system, the waste heat recovery system of the present application preferably comprises a one-way explosion-proof valve, which is preferably arranged downstream of the cooling and washing device, more specifically between the cooling and washing device and the deoxidizing device. If backfire occurs through the pipeline during ignition or combustion, the one-way explosion-proof valve can prevent the cooling and washing device and the upstream system from exploding due to backfire, thereby cutting off the process and avoiding affecting the operation of the titanium tetrachloride main production system due to backfire.

[0046] Flue gas preheater The flue gas preheater is not necessary for the waste heat recovery system of the present application. However, in order to make the chlorinated flue gas entering the deoxidizing device reach a suitable temperature, the waste heat recovery system of the present application preferably further comprises a flue gas preheater, which is located downstream of the cooling and washing device and upstream of the deoxidizing device and communicates with both. When a one-way explosion-proof valve is arranged, the flue gas preheater is arranged between the one-way explosion-proof valve and the deoxidizing device.

[0047] The flue gas preheater can utilize various suitable means to preheat the chlorination flue gas. However, it is preferred to utilize the waste heat of the chlorination flue gas from the waste heat recovery subsystem to preheat the chlorination flue gas. For example, a majority of the chlorination flue gas from the waste heat boiler of the waste heat recovery subsystem goes to the downstream device, but a small portion of the flue gas can be recycled (e.g., by a fan, preferably a high temperature fan) to the flue gas preheater to further utilize the waste heat of the chlorination flue gas. This portion of the recycled flue gas can be directly discharged to the chimney after exiting the flue gas preheater, but is preferably recycled to the waste heat boiler. More specifically, the chlorination flue gas from the cooling and washing device is at a low temperature (e.g., about 20 degrees Celsius), and preheating the flue gas from the cooling and washing device as the main stream by utilizing the heat of a portion of the flue gas from the waste heat recovery subsystem that is involved in the internal circulation can provide heat in advance to the subsequent processes (e.g., oxygen removal, catalytic combustion, etc.), thereby further improving the waste heat recovery efficiency.

[0048] Oxygen removal device The oxygen removal device is not particularly limited in the present application, and any device that can be used to remove oxygen from the chlorination flue gas can be used in the waste heat recovery system of the present application, such as an adsorption oxygen removal device and a catalytic oxygen removal device, preferably a low temperature (i.e., a temperature lower than the normal reaction temperature, e.g., 100 to 300 degrees Celsius) catalytic oxygen removal device.

[0049] The adsorption oxygen removal device directly utilizes some porous adsorption material to adsorb oxygen, and then the distance between the oxygen removal device and the catalytic combustion subsystem is set to be relatively long, so that the oxygen concentration near the fire source is extremely low and it is impossible to transmit back to the fire to cause explosion, thereby ensuring the safety of the upstream. For example, porous adsorption materials such as tetracyanoquinodimethane (TCNQ) can be used, since such materials only react with the electrons of oxygen in the air, and only oxygen molecules can be adsorbed into the small pores of such materials, thereby facilitating the separation of oxygen in the air. Of course, other materials that can reduce the oxygen content can also be selected. However, such oxygen removal devices are relatively high in cost compared to catalytic oxygen removal devices.

[0050] The catalytic oxygen removal device preferably uses honeycomb-shaped ceramic as the carrier (preferably honeycomb-shaped cordierite), and then coats noble metals (preferably platinum) as the active component, and the amount of noble metals is controlled to enable the reaction of carbon monoxide with oxygen at a relatively low temperature (e.g., 100 to 300 degrees Celsius) that is lower than the ignition point of carbon monoxide (normal concentration of carbon monoxide at normal pressure is about 650 degrees Celsius), thereby consuming oxygen in the form of flameless combustion. Since it is flameless combustion, it will not cause backfire explosion.

[0051] Catalytic combustion subsystem The catalytic combustion sub-system is not particularly limited, and any device capable of catalytically combusting the chlorinated flue gas can be used in the waste heat recovery system of the present application. When the carbon monoxide content in the chlorinated flue gas is less than 20%, the flue gas is generally not ignitable due to insufficient heat value, and the ignition temperature is very high (at 850 to 950 °C). The catalytic combustion sub-system is required to ignite the flue gas by using a catalyst, and the ignition temperature after catalysis can be controlled to more than 600 °C.

[0052] The catalytic combustion sub-system can catalyze the combustion and oxidation of carbon monoxide in the flue gas with oxygen in the air even when the carbon monoxide concentration in the flue gas is low, and the resulting carbon dioxide is discharged. The present application preferably uses a COC catalyst (i.e., a catalyst having a honeycomb-shaped ceramic carrier and an active component capable of catalyzing the oxidation of carbon monoxide to carbon dioxide coated on the carrier) to promote combustion, and the reaction temperature range can be 600 to 800 °C to improve the combustion efficiency of the flue gas. The active component can be a noble metal or a transition metal oxide, which lowers the activation energy of the reaction to allow the reaction to proceed rapidly under relatively mild conditions. Platinum is more preferred as the active component. The honeycomb-shaped ceramic carrier of the active component itself acts as a heat accumulator. After the flue gas flows through the heat accumulator, a portion of the heat is left in the heat accumulator, so that the heat accumulator is always maintained at a high temperature (e.g., about 600 to 800 °C). Even if the temperature of the flue gas before entering the catalytic combustion barrel is low, the flue gas can be ignited when it flows through the high-temperature heat accumulator, so that the carbon monoxide is combusted to form carbon dioxide.

[0053] The catalyst used in the catalytic combustion sub-system and the catalyst used in the oxygen removal device can be selected from substantially the same materials, but the amount of active component used in the oxygen removal device is significantly higher than that used in the catalytic combustion sub-system to ensure that the oxidation reaction (to reduce the oxygen content in the flue gas to less than 1 vol%) is achieved at a low temperature (e.g., about 150 to 300 °C) in the oxygen removal device, and the amount of catalyst used in the catalytic combustion sub-system is correspondingly low, and is preferably controlled to an amount that can catalyze the combustion reaction of carbon monoxide and oxygen at a temperature range of 600 to 800 °C.

[0054] According to some embodiments, the catalytic combustion sub-system comprises a make-up natural gas inlet for supplementing natural gas. The carbon monoxide content in chlorinated flue gas normally fluctuates between 8-20 vol%, but is basically around 14-16 vol%, at which point no additional natural gas for co-combustion is needed. However, for cases where the carbon monoxide content in chlorinated flue gas is relatively low (e.g. below 14 vol%), the heat value is not enough and the ignition temperature is too high, so additional co-combustion of natural gas is beneficial for igniting the flue gas. In addition, theoretically, for chlorinated flue gas with carbon monoxide content below 16 vol%, supplementing natural gas for co-combustion is beneficial for the complete combustion of carbon monoxide. Furthermore, natural gas is also needed to be introduced to ignite the system at the initial start-up. Therefore, it is preferred that a make-up natural gas inlet is provided in the catalytic combustion sub-system in the system of the present application.

[0055] According to some embodiments, the catalytic combustion barrel further comprises honeycomb ceramic inside, which can store the residual heat from the previous round of combustion. The honeycomb ceramic acts as a heat storage body, which can maintain a high temperature, so that the flue gas can be combusted under the action of the catalyst at a temperature higher than the inlet temperature of the burner (i.e. high-temperature heat storage catalytic combustion). In this case, the catalytic combustion barrel is a high-temperature heat storage catalytic combustion barrel with a heat storage body (honeycomb ceramic), which is more beneficial for dealing with cases where the heat value of chlorinated flue gas is unstable. Specifically, the carbon monoxide content in chlorinated flue gas normally fluctuates between 8-20 vol%. For cases where the carbon monoxide content in chlorinated flue gas is relatively high (e.g. above 14 vol%), the flue gas can still be basically combusted normally even without a heat storage body. However, for cases where the carbon monoxide content in chlorinated flue gas is relatively low, the heat value is low, so the use of a heat storage body can warm up the chlorinated flue gas and thus facilitate its combustion.

[0056] In addition, since the carbon monoxide content in chlorinated flue gas normally fluctuates between 8-20 vol%, and the heat value is not enough when the carbon monoxide content in the flue gas is below 14 vol%, the ignition temperature is very high (about 850-950°C). Therefore, a catalyst needs to be used to lower the ignition temperature to ignite the flue gas, for example, the ignition temperature can be controlled to about 600-800°C under the action of the catalyst. A particularly suitable catalyst is as described above.

[0057] The high-temperature heat storage catalytic combustion barrel can be arranged next to the waste heat boiler.

[0058] Waste heat recovery sub-system The waste heat recovery sub-system used in the present application can be those conventional in the prior art, such as a waste heat boiler. The waste heat boiler can use the heat generated by the combustion of carbon monoxide to produce steam, achieving the purpose of waste heat recovery.

[0059] A waste heat recovery subsystem particularly suitable for use in the present application comprises a waste heat boiler. The waste heat boiler recovers waste heat from the chlorination flue gas to generate steam and to export the steam, thereby achieving the purpose of waste heat recovery. The waste heat boiler can be a boiler capable of directly heating water to steam and exporting the steam, or a waste heat boiler provided with a steam drum connected thereto. Preferably, the waste heat boiler is provided with a steam drum. The water used is preferably desalinated water, which can be directly taken from a desalinated water pipe network, or can be taken from the desalinated water pipe network first through a feed water preheater before being fed into the waste heat recovery subsystem (e.g. into the steam drum). The desalinated water can be transported using a high pressure difference, but is preferably pumped from the desalinated water pipe network using a water pump. The waste heat boiler heats the water from the steam drum and flowing through the heat exchange pipes provided inside the boiler to become water vapor and is exported. More specifically, the steam drum continuously outputs steam, and the boiler feed water pump continuously pumps make-up water to maintain a dynamic balance, which is equivalent to the waste heat boiler directly heating the water in the steam drum to become steam. The waste heat boiler and the catalytic combustion barrel are arranged in close proximity so that the heat generated by combustion can directly heat the waste heat boiler. The catalytic combustion barrel is connected to the flue gas inlet of the waste heat boiler through at least one flue gas outlet pipe with a large flux. The make-up desalinated water can be directly fed into the waste heat boiler, or can be fed into the heat exchange pipes of the waste heat boiler through the steam drum via a make-up water pipe.

[0060] Air preheater and feed water preheater If the chlorination flue gas still has a relatively high temperature after being processed by the waste heat recovery subsystem, in order to further recover the waste heat of the chlorination flue gas, an air preheater and / or a feed water preheater can be provided downstream of the waste heat recovery subsystem. The air preheater can use the heat of the flue gas from the waste heat recovery subsystem to preheat air and feed the preheated air into the catalytic combustion subsystem. The feed water preheater can use the heat of the flue gas from the waste heat recovery subsystem to preheat desalinated water and feed the preheated desalinated water into the waste heat recovery subsystem, for example into the steam drum connected to the waste heat boiler. According to some embodiments, the waste heat recovery system of the present application simultaneously comprises an air preheater and a feed water preheater, and the feed water preheater is located downstream of the air preheater. In general, the temperature of the flue gas from the waste heat recovery subsystem (e.g. the waste heat boiler) can still be as high as more than two hundred degrees Celsius, after being heated by the air preheater, the temperature of the flue gas continues to drop, for example to about one hundred and fifty degrees Celsius, and then enters the feed water preheater to heat the desalinated water (e.g. to about forty to seventy degrees Celsius), and then the heated desalinated water is sent to the steam drum via a pipeline to supplement hot water.

[0061] It should be understood that the directional terms such as "upper," "lower," "front," and "rear," as well as the morphological terms such as "rod," "box," and "piece," used herein, are merely for the purpose of explaining the present invention in conjunction with the accompanying drawings and do not constitute, and cannot be used to limit, the present invention. All directional indications in the embodiments of this application are intended only to explain the relative positional relationships and movement of components in a specific posture. If the specific posture changes, the directional indications will also change accordingly. In this application, unless otherwise expressly specified or limited, the terms "connected," "connected," and "fixed" should be understood broadly. For example, "fixed" can refer to a fixed connection, a detachable connection, or integration; it can refer to a direct connection or an indirect connection through an intermediate medium; it can refer to internal communication between two components or an interaction between two components, unless otherwise expressly limited. Those skilled in the art will understand the specific meanings of the above terms in this application based on the specific circumstances. Furthermore, references to "first," "second," and the like in this application are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features indicated. Therefore, features defined as "first" or "second" may explicitly or implicitly include at least one of these features. Furthermore, technical features of various embodiments may be combined, but this must be based on the ability of a person of ordinary skill in the art to implement them. If the combination of technical features contradicts or cannot be implemented, such combination shall be deemed non-existent and not within the scope of protection claimed in this application.

[0062] In order to make the technical solution of the present invention clearer, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0063] Example 1: Waste Heat Recovery System like Figure 1 As shown, the flue gas waste heat recovery system of the present invention includes a pretreatment subsystem 1 (for the pretreatment process), a cooling and washing device 2 (for the pneumatic emulsification process), a deoxidation device 3 (for the catalytic deoxidation process), a catalytic combustion subsystem 4 (for the catalytic combustion process), and a waste heat recovery subsystem 5 (for waste heat recovery) connected in series.

[0064] like Figure 2 and Figure 3As shown, the chlorinated flue gas from the titanium tetrachloride production process is pretreated in sequence by passing through the first gas-liquid separator 101, the spray device 102, and the second gas-liquid separator 103 of the pretreatment subsystem 1. It is then cooled, dehumidified, and flame-retarded by the cooling and scrubbing device 2 (a cyclone water seal fire-retardant device). The cooling and dehumidified chlorinated flue gas is passed through the one-way explosion-proof valve 8 to the flue gas preheater 7 for preheating. It is then passed through the deoxygenation device 3 (specifically, a catalytic deoxygenation device) for deoxygenation. The deoxygenated chlorinated flue gas is passed through the catalytic combustion subsystem 4 and reacts with air from the outside (natural gas is optionally supplemented) to burn and generate carbon dioxide. The chlorinated flue gas is then passed through the waste heat boiler 501 of the waste heat recovery subsystem 5 and its heat is used to generate steam from the boiler water. The steam is then transported outward after passing through the steam drum 502. A small portion of the chlorinated flue gas from the waste heat boiler 501 is blown by a fan (specifically, a high-pressure fan, Figure 2 The flue gas (not shown) is sent to the flue gas preheater 7 to preheat the mainstream flue gas in the flue gas preheater 7 and circulate it to the waste heat boiler 501. The remaining majority continues to pass into the air preheater 508 and preheats the outside air through heat exchange. The air preheated by the air preheater 508 is passed into the catalytic combustion subsystem 4. The chlorinated flue gas from the air preheater 508 continues to pass into the feed water preheater 503 and preheats the desalted water through heat exchange. The desalted water is pumped into the feed water preheater 503 by two parallel feed water pumps 505. The desalted water preheated by the feed water preheater 503 is passed into the steam drum 502. The chlorinated flue gas from the feed water preheater 503 passes through the dust collector 504 and is discharged into the chimney 6. A system bypass is provided before the cooling and washing device 2 to allow the chlorinated flue gas to be discharged into the chimney 6 through the system bypass in an emergency. The waste heat recovery system of this embodiment can fully recover and utilize the calorific value of the chlorinated flue gas and ensure the safety of the main system.

[0065] Example 2: Waste Heat Recovery System The waste heat recovery system of Example 2 is essentially the same as that of Example 1, except that the deoxygenation device is not a catalytic deoxygenation device, but an adsorption deoxygenation device, in which tetracyanoquinodimethane (TCNQ) is used as the porous adsorption material. Accordingly, the length of the pipeline between the deoxygenation device and the catalytic combustion subsystem is significantly extended, resulting in an extremely low oxygen concentration near the fire source, making it impossible to transfer back the fire and cause an explosion, thus ensuring upstream safety. The waste heat recovery system of this embodiment can fully recover and utilize the calorific value of the chlorinated flue gas and ensure the safety of the main system. However, the deoxygenation cost of the adsorption deoxygenation device is relatively high, and extending the pipeline length to ensure safety also increases costs.

[0066] Example 3: Waste Heat Recovery System like Figure 3As shown, the chlorination flue gas (temperature -10 to 0℃) from the titanium tetrachloride production process, after the first gas-liquid separator 101 (valve is provided after the first gas-liquid separator 101), passes through the three-stage series water spray device 1021 and the two-stage series alkali spray device 1022 in turn, and then passes through the second gas-liquid separator 103, and is introduced into the cooling scrubbing device 2 in turn by the induced draft fan 104, the main road electric valve 105, the pressure detection instrument (not shown in the figure) and the booster fan 107 (boosted to 1500 Pa). The first gas-liquid separation can separate out liquid droplets and solid impurities, the water spray can make chlorine in the flue gas generate hydrochloric acid, the alkali spray can neutralize the hydrochloric acid and remove the hydrochloric acid and sulfides, and the second gas-liquid separation can further separate out liquid droplets.

[0067] A system bypass directly leading to the chimney 6 is provided between the induced draft fan 104 and the main road electric valve 105, and the system bypass electric valve 106 is provided in the system bypass. The system bypass electric valve 106 is normally closed, and can be opened to shut off the process when needed (for example, in the case of parking or emergency), so that the chlorination flue gas does not enter the subsequent process, but is directly discharged from the chimney 6.

[0068] The cooling scrubbing device 2 includes a cyclone (cyclone explosion-proof valve, 1500 Pa), which can cool and scrub the flue gas in a pneumatic emulsification manner and achieve water sealing and fire blocking, thereby playing the role of an explosion-proof valve. The cooling scrubbing device 2 uses water as a heat exchange medium, and the water entering the inlet of the cooling scrubbing device 2 has a temperature of 20℃, and the water exiting the outlet has a temperature of 40℃. The 40℃ water from the cooling scrubbing device 2 is circulated by the heat exchanger circulating pump 203 (3m 3The water medium from the heat exchanger 201 (such as GGH condenser) is heated by the heat exchange with the chilled brine (0 degree Celsius) from the chilled brine system 202. After the heat exchange, the outlet temperature of the chilled brine and the water medium from the heat exchanger 201 is 20 degree Celsius, and the chilled brine is circulated to the chilled brine system 202, and the water medium is circulated to the cooling and washing device 2. The flue gas (oxygen content is 2-3 vol%) from the cooling and washing device 2 enters the oxygen removal device 3 (specifically, a catalytic oxygen removal device) in sequence through the one-way explosion-proof valve 8 and the flue gas preheater 7. If backfire occurs during ignition or combustion, the one-way explosion-proof valve 8 can prevent the cooling and washing device 2 and the upstream system from exploding due to backfire, thereby cutting off the process and avoiding the influence of backfire on the operation of the titanium tetrachloride main production system. The flue gas preheater 7 uses a small part (such as 10%) of the high-temperature flue gas (a control valve is arranged in the pipeline) from the waste heat boiler 501 to preheat the flue gas in the main flow path, and the flue gas preheated by the flue gas preheater 7 is used to preheat the catalytic oxygen removal device, and the flue gas from the waste heat boiler 501 for preheating is circulated to the waste heat boiler 507 through the fan 507 (specifically, a high-temperature fan). After being preheated, the flue gas is removed by the catalytic oxygen removal device, and the oxygen content is reduced from 2-3 vol% to less than 1 vol%.

[0069] The flue gas from the catalytic oxygen removal device enters the catalytic combustion barrel with heat storage body for catalytic combustion, and the carbon monoxide in the flue gas reacts with the oxygen in the fresh high-temperature air (120 degree Celsius) from the air preheater 508 to generate carbon dioxide and release heat. The catalytic combustion barrel has a honeycomb-shaped ceramic as a heat storage body, which can store the waste heat of the previous round of combustion. This device is beneficial to deal with the situation that the heat value of chlorination flue gas is unstable (such as the temperature of flue gas is low due to fluctuation). After flowing through the heat storage body, the flue gas leaves part of the heat in the heat storage body, so that the heat storage body is always maintained at a high temperature (more than 600 degrees Celsius). Even if the temperature of the flue gas before entering the catalytic combustion barrel is low, the flue gas can be ignited when flowing through the high-temperature heat storage body, so that the carbon monoxide is combusted to generate carbon dioxide. The catalyst used in the high-temperature heat storage catalytic combustion barrel can reduce the ignition temperature to ignite the flue gas, and the catalyst can control the ignition temperature to be more than 600 degrees Celsius. The catalyst uses a honeycomb-shaped ceramic as a carrier, and an active component (Pt) is coated on the carrier at high temperature, which can treat the carbon monoxide generated by incomplete combustion at a reaction temperature range of 600-800 degrees Celsius to generate carbon dioxide. The honeycomb-shaped ceramic carrier of the catalyst can also act as a heat storage body.

[0070] In order to deal with the situation that the content of carbon monoxide in the flue gas is too low, the catalytic combustion barrel is provided with a supplementary natural gas inlet and a corresponding pipeline (the flow of the supplementary natural gas is 125 Nm 3 / h), and the supplementary natural gas can be used for accompanying combustion when needed.

[0071] The catalytic combustion barrel is adjacent to the waste heat boiler 501 and is connected with the waste heat boiler 501 through two flue gas outlet pipes of the catalytic combustion barrel, so that the heat generated by combustion of flue gas in the catalytic combustion barrel can be immediately used for heating the waste heat boiler 501. The waste heat boiler 501 converts water in a steam drum 502 connected with the waste heat boiler 501 into steam (4 t / h) by heat exchange between the water and high-temperature flue gas through a serpentine pipe inside the boiler, thereby realizing recycling of heat.

[0072] Except that a small part (for example, 10%) of flue gas from the waste heat boiler 501 is circulated to the waste heat boiler 501 by passing through the flue gas preheater 7, most of flue gas (11500 Nm 3 / h) discharged from the boiler is sequentially passed through the air preheater 508 and the feed water preheater 503 downstream. The air preheater 508 can preheat fresh air (20 degrees Celsius, 5500 m 3 / h) sent from outside through the air blower 506 to 120 degrees Celsius and send the fresh air into the catalytic combustion barrel. The feed water preheater 503 can preheat desalted water pumped from a desalted water pipe network through two parallel feed water pumps 505, and the preheated desalted water is used as boiler makeup water and is passed into the steam drum 502 connected with the waste heat boiler 501.

[0073] Flue gas from the feed water preheater 503 is passed into the dust collector 504 for dust removal, and the dust-removed flue gas (100 degrees Celsius, 15700 m 3 / h) is passed into the chimney 6 for discharge. A flue gas detection device is installed at the discharge port of the chimney 6 to ensure that the flue gas meets the relevant emission standards and to monitor the treatment effect of the system.

[0074] The process of the embodiment is proved to be able to output steam at an average flow rate of 4 t / h and to ensure the safety of the waste heat recovery system and the titanium tetrachloride main production system. In addition, since the system bypass is provided, even if the waste heat recovery system needs to be shut down for maintenance, the normal operation of the titanium tetrachloride main production system will not be affected.

[0075] The flue gas waste heat recovery system of the present application realizes efficient and safe comprehensive utilization of chlorination flue gas, and effectively improves the safety, stability and effectiveness of the entire system through system design.

[0076] The above-described embodiments only express several embodiments of the present application, and the description is relatively specific and detailed, but it should not be understood as a limitation on the scope of the patent of the present application. It should be noted that, for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A chlorinated flue gas waste heat recovery process, which comprises the following steps in sequence: (a) pre-treating the chlorinated flue gas from the titanium tetrachloride production process in a pre-treatment subsystem (1) to remove titanium tetrachloride, a portion of sulfur dioxide and hydrogen chloride; (b) cooling and washing the chlorinated flue gas in a cooling and washing device (2); (c) deoxidizing the chlorinated flue gas in a deoxidizing device (3); (d) catalytically burning the chlorinated flue gas in a catalytic combustion subsystem (4); and (e) recovering waste heat in a waste heat recovery subsystem (5); wherein the pre-treatment in step (a) comprises the following sub-steps in sequence: washing with chilled water to condense and cool the chlorinated flue gas to precipitate titanium tetrachloride droplets; performing a first gas-liquid separation in a first gas-liquid separator (101) to separate the droplets and solid impurities; and performing a water spraying device ( 1021) is sprayed with water to generate hydrochloric acid from chlorine in the flue gas; alkali is sprayed through the alkali spray device (1022) to neutralize the hydrochloric acid and remove hydrochloric acid droplets and sulfur dioxide; a second gas-liquid separation is performed through the second gas-liquid separator (103) to further condense the droplets from the spray device (102) and collect them again; a system bypass is connected to the pipeline between the pretreatment subsystem (1) and the cooling and washing device (2), and an electric valve (106) is set on the system bypass; a one-way explosion-proof valve (8) is set on the pipeline between the cooling and washing device (2) and the deoxidation device (3); a waste heat boiler (501) with a steam drum (502) connected thereto is set in the waste heat recovery subsystem (5), and the waste heat boiler (501) uses the heat of the flue gas to heat the feed water and transmits steam to the outside through the steam drum (502).

2. The chlorinated flue gas waste heat recovery process according to claim 1, characterized in that A flue gas preheater (7) is provided on the pipeline between the one-way explosion-proof valve (8) and the deaerator (3). The flue gas preheater (7) uses a portion of the flue gas from step (e) to preheat the mainstream flue gas to be introduced into step (c), and the chlorinated flue gas whose temperature is reduced by the flue gas preheater (7) is circulated to the waste heat boiler (501) or discharged into the chimney.

3. The chlorinated flue gas waste heat recovery process according to claim 1, characterized in that: The chlorinated flue gas from step (a) is passed through a pressure detection instrument and a booster fan (107) into a cooling and washing device (2).

4. The chlorinated flue gas waste heat recovery process according to claim 1, characterized in that: The deoxygenation in step (c) is adsorption deoxygenation, using porous adsorption material as an adsorbent to adsorb oxygen in the flue gas.

5. The chlorinated flue gas waste heat recovery process according to claim 1, characterized in that: The catalytic combustion in step (d) is carried out in a catalytic combustion barrel containing honeycomb-shaped ceramics as a heat storage body.

6. The chlorinated flue gas waste heat recovery process according to claim 1, characterized in that: The catalyst in step (d) uses a honeycomb-shaped ceramic as a carrier, and the carrier is coated with an active component, which is a noble metal or a transition metal oxide.

7. The chlorinated flue gas waste heat recovery process according to claim 1, characterized in that: In step (d), combustion is assisted by adding a portion of natural gas.

8. The chlorinated flue gas waste heat recovery process according to claim 1, characterized in that: The deoxygenation device (3) is a catalytic deoxygenation device capable of causing carbon monoxide to undergo an oxidation reaction at a temperature of 150-300 degrees Celsius.

9. The chlorinated flue gas waste heat recovery process according to claim 8, characterized in that: The catalyst used in the catalytic deoxidation device is a catalyst using honeycomb-shaped ceramics as a carrier and platinum metal as an active component.

10. The chlorinated flue gas waste heat recovery process according to claim 9, characterized in that: The honeycomb-shaped ceramic is cordierite.

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