CN214914693U - Built-in heating integrated device for continuously adsorbing and desorbing organic waste gas - Google Patents

Built-in heating integrated device for continuously adsorbing and desorbing organic waste gas Download PDF

Info

Publication number
CN214914693U
CN214914693U CN202022163471.8U CN202022163471U CN214914693U CN 214914693 U CN214914693 U CN 214914693U CN 202022163471 U CN202022163471 U CN 202022163471U CN 214914693 U CN214914693 U CN 214914693U
Authority
CN
China
Prior art keywords
built
activated carbon
waste gas
organic waste
electric heating
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Fee Related
Application number
CN202022163471.8U
Other languages
Chinese (zh)
Inventor
李坤豪
刘小飞
赵仕沛
贾晓蕾
吴瑞杰
赵大林
贾婷婷
孙雷
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Henan Environmental Protection Research Institute
Henan General Institute Of Geological Surveying And Mapping
Original Assignee
Henan Environmental Protection Research Institute
Henan General Institute Of Geological Surveying And Mapping
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Henan Environmental Protection Research Institute, Henan General Institute Of Geological Surveying And Mapping filed Critical Henan Environmental Protection Research Institute
Priority to CN202022163471.8U priority Critical patent/CN214914693U/en
Application granted granted Critical
Publication of CN214914693U publication Critical patent/CN214914693U/en
Expired - Fee Related legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Images

Landscapes

  • Treating Waste Gases (AREA)

Abstract

The utility model relates to a device of desorption organic waste gas is adsorbed in succession in built-in heating integration belongs to organic waste gas treatment equipment field, the device includes outer parcel of alloy, inside support frame, honeycomb active carbon module, built-in electric heater unit, gaseous redistribution district, on-line monitoring probe, control system, fan. The utility model discloses an integrated device with adsorb in succession and desorption, the design is dexterous, the operation of being convenient for, has the electrical heating cover and the honeycomb active carbon adsorption integrated device who is used for the desorption, has reduced and has established heating device's occupation of land and cost in addition, and built-in heat transfer plate has increased heat utilization efficiency simultaneously, has improved the efficiency of active carbon desorption organic waste gas, is applicable to the improvement of industrial organic waste gas such as printing, surface coating, furniture manufacturing and wood working.

Description

Built-in heating integrated device for continuously adsorbing and desorbing organic waste gas
Technical Field
The utility model relates to a device of desorption organic waste gas is adsorbed in succession in built-in heating integration belongs to organic waste gas treatment equipment field, is applicable to the improvement of industry organic waste gas such as printing, surface coating, furniture manufacturing and wood working.
Background
Organic waste gas is a kind of waste gas with various kinds and complex components. It comprises hydrocarbons (alkane, alkene, alkyne, aliphatic hydrocarbon, alicyclic hydrocarbon, aromatic hydrocarbon and polycyclic aromatic hydrocarbon); oxygen-containing organic substances (phenols, aldehydes, ketones, organic acids); chlorinated organics (vinyl chloride, methyl chloride, ethylene dichloride, chlorohydrin); nitrogen-containing organic substances (amine compounds, acrylonitrile, acrylon); sulfur-containing organics (mercaptans, thiophenes, carbon disulfide). These waste gases originate from a very wide variety of sources from the organic synthesis industry, the petrochemical industry, motor vehicles and industrial sectors using processed organic products. Organic waste gas is harmful, for example, gaseous hydrocarbon discharged into the atmosphere reaches a certain amount, and photochemical reaction can occur under the action of sunlight; some components in the organic waste gas, such as benzocastor, dibenzocastor, benzanthracene, dibenzoanthracene, anthracene, etc., are carcinogenic substances, and some are strong carcinogenic substances. Therefore, the discharge and purification of organic waste gas have been attracting attention. The adsorption method has high purification efficiency, can recover organic substances, and is commonly used for purifying low-concentration organic waste gas. This method can be used alone or in combination with other methods.
Different purification and recovery methods can be used depending on the nature, characteristics and environment of the organic waste gas, and the possibility of recovering the organic substances therein. Generally, an adsorption method, a combustion method, a liquid absorption method, a condensation method, and the like are used. When the adsorption method is used, an adsorption phenomenon occurs when an organic gas comes into contact with the surface of an adsorbent. Usually, the adsorption is physical adsorption in the organic waste gas purification process, and the adsorption process is reversible. After saturation of the adsorption, the adsorbate can be removed from the surface of the adsorbent by heating or other means to restore the original state. This process is called desorption or desorption. By utilizing the desorption, the recovery of organic matters and the regeneration of the adsorbent can be carried out.
At present, the device of organic waste gas adsorption and desorption adopts heating device and adsorption and desorption disconnect-type device more, and the hot-air need carry out the thermal desorption in carrying to adsorption equipment through external pipeline after the heating, and the heat is inevitable loses in transportation process, causes the desorption effect to descend. In summary, the existing heating device and the adsorption-desorption separation device need to be improved to reduce heat loss and improve desorption efficiency.
SUMMERY OF THE UTILITY MODEL
The utility model aims to solve the technical problem that to the not enough of above-mentioned disconnect-type device, provide a device of desorption organic waste gas is adsorbed in succession in built-in heating integration, be equipped with built-in inclosed heating device dismantled all around simultaneously, both dismantle the maintenance and maintain convenient, avoid gaseous short circuit, the entering heating region that leaks at the active carbon propulsion in-process again, whole device has advantages such as heat transfer efficiency is high, quick detachable, desorption effect are good.
The utility model discloses a built-in heating integrated device for continuously adsorbing and desorbing organic waste gas, which comprises an alloy outer wrapping, an inner supporting frame and a honeycomb activated carbon module; the system comprises a built-in electric heating device, a gas redistribution area, an online monitoring probe, a control system, a fan, an air inlet hood, an air outlet hood, an exhaust funnel and a combustion device; wherein the content of the first and second substances,
the alloy outer wrapping layer is arranged on the outermost layer of the adsorption device;
the internal support frame is arranged in the whole device;
the honeycomb activated carbon module is arranged around the heat transfer plate and the heating sleeve, the heating sleeve is arranged at the center, and the heat transfer plate is arranged at the center or the gas redistribution area;
the built-in electric heating sleeve is arranged on the innermost layer of the whole device;
the built-in heat transfer plate is arranged between the internal support frame and the heating sleeve;
the gas redistribution area is arranged at the tail end of each stage of honeycomb activated carbon;
the online monitoring probe is arranged at the tail end of the last stage of honeycomb activated carbon;
the control system is an external system and is used for controlling the temperature controller and the online monitoring probe;
the fan is arranged at one end of the honeycomb activated carbon adsorption device.
Preferably, the alloy outer package comprises a side surface closed package of the adsorption device, an A-end air inlet cover, an A-end heating sleeve closed cover, a B-end air outlet cover, a heating sleeve closed cover and a temperature controller.
Preferably, the inner support frame and the alloy outer wrapping are welded into a whole.
Preferably, the honeycomb activated carbon module comprises three to four honeycomb activated carbon bed layers which are sequentially laid on the internal support frame.
Preferably, the built-in electric heating sleeve is placed on the internal support frame through the heat transfer plate, is not fixed and is convenient for later-stage taking out and maintenance, and the interior of the built-in electric heating sleeve is hollow to form hot air; heating sealing covers are arranged at two ends of the heating sleeve.
Preferably, the built-in heat transfer plate is arranged between the internal support frame and the heating sleeve, the built-in heat transfer plate and the internal support frame are not fixed, so that the built-in heat transfer plate is convenient to take out and maintain at a later stage, and is directly connected with the heating sleeve to obtain heat; the two ends of the heating plate heat the closed cover.
Preferably, the gas redistribution area comprises three to four layers of gas redistribution areas (heat transfer plates can be configured in the area), and a length space of 5-10cm is reserved in each layer of gas redistribution area, so that the gas is uniformly mixed again at the area and then enters the next layer of activated carbon for adsorption and purification, the utilization rate of the next layer of activated carbon can be improved, the adsorption efficiency is improved, and the early saturation of the activated carbon is delayed.
Preferably, the on-line monitoring probe is used for monitoring the standard reaching condition of the organic waste gas after tail end waste gas purification, and timely starting the heating system and the desorption system.
Preferably, the control system is an external system and is used for controlling the valve, the temperature and the online monitoring system, starting the thermal desorption system in time according to monitoring data, closing the waste gas inlet valve and opening the thermal desorption valve; and when the concentration is judged to be larger, the system starts to act, the air inlet valve of the branch is closed, the air inlet valve of the other branch is opened, and the purified air outlet valve is correspondingly closed and opened.
Preferably, the fan is arranged at one end of the honeycomb activated carbon adsorption device and used for sucking hot air formed in the heating sleeve into the activated carbon bed layer for desorption operation.
When the on-line monitoring probe works, the control system sends an instruction by detecting whether the purified waste gas meets the standard requirement, switches A, B valves at two ends, and switches adsorption and desorption of an activated carbon bed layer to work alternately, so that continuous operation is realized; the control system sends out an instruction, when the upper activated carbon layer is saturated in adsorption, the first air inlet valve closes the first air outlet valve, the heating system is started, when the set desorption temperature is reached, the first thermal desorption valve is opened, the first combustion air inlet valve is opened at the same time, and the second fan is started to enter the combustion device for purification and then be discharged; meanwhile, starting the lower-layer activated carbon adsorption system, starting a second air inlet valve of the other branch, and starting a second air outlet valve, wherein the first combustion air inlet valve is in a closed state; the above operations are repeated to achieve the purpose of continuous operation.
Compared with the prior art, the utility model discloses following technological effect has: the utility model discloses a device of desorption organic waste gas is adsorbed in succession in built-in heating integration is equipped with built-in inclosed heating device dismantled all around simultaneously, has both dismantled the maintenance and has maintained the convenience, avoids gaseous short circuit, the entering heating region that leaks at active carbon propulsion in-process again, and whole device has advantages such as heat transfer efficiency is high, quick detachable, desorption effect is good.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are required to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained from the drawings without inventive effort.
Fig. 1 is the utility model relates to a built-in heating integration adsorbs in succession the structural schematic diagram of desorption organic waste gas's device.
Fig. 2 is the utility model relates to a side appearance of the device of continuous adsorption and desorption organic waste gas of built-in heating integration.
Fig. 3 is a diagram of the two ends (after the sealing cover is removed) of the device for continuously adsorbing and desorbing organic waste gas with integrated heating.
Reference numerals:
the device comprises a device 1, an alloy outer wrapping 2, an inner support frame 3, a honeycomb activated carbon module 4, a built-in electric heating device 5, a gas redistribution area 6, an online monitoring probe 7, a control system 8, a first fan 9, a combustion device 10, a first air inlet valve 11, a second air inlet valve 12, a temperature controller 13, a heat transfer plate 14, a heating sleeve 15, a first air outlet valve 16, a second air outlet valve 17, an exhaust funnel 18, an inner vertical support frame 19, an inner horizontal support frame 20, a second fan 21, a first thermal desorption valve 22, a second thermal desorption valve 23, a first combustion air inlet valve 24, a first combustion air inlet valve 25, a side air inlet valve 26, an outer cover 27 which can be disassembled on the side surface of a heating area, an A-end heating seal cover 28 and a B-end heating seal cover 29
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some embodiments of the present application, but not all embodiments. The components of the embodiments of the present application, generally described and illustrated in the figures herein, can be arranged and designed in a wide variety of different configurations.
As shown in fig. 1, the utility model discloses a device 1 of desorption organic waste gas is adsorbed in succession in built-in heating integration, include: the alloy outer wrapping 2, the inner supporting frame 3 and the honeycomb activated carbon module 4; the system comprises a built-in electric heating device 5, a gas redistribution area 6, an online monitoring probe 7, a control system 8, a fan, an air inlet hood, an air outlet hood, an exhaust funnel 18 and a combustion device 10;
the outer alloy wrapping 2 comprises an A-end air inlet cover, a B-end air outlet cover and a heating area side surface detachable outer cover 27, the inner support frame 3 is provided with a horizontal support frame 20 and a vertical support frame 19, and the honeycomb activated carbon module 4 is arranged on the inner support frame 3; the alloy outer wrapping layer 2 is divided into an upper bed layer and a lower bed layer, each bed layer is separated by an inner vertical supporting frame 19, the vertical supporting frames are arranged into a plate shape, an electric heating device 5 is arranged in each bed layer, a gas redistribution area 6 is positioned behind a honeycomb activated carbon module 4, an online monitoring probe 7 is arranged at the end B, a control system 8 is a control source of the device, a fan 9 is arranged at two ends of the device, and the device is fixed after position adjustment is finished.
The alloy outer wrapping 2 comprises an air inlet cover and an air outlet cover with valves and is used for controlling the entering of waste gas, the discharging of purified gas and the desorption discharging of concentrated desorption gas, a horizontal partition plate is arranged in each cover and is used for isolating the inlet and the outlet of the upper and the lower activated carbon beds, and the continuous work of adsorption and desorption is facilitated; the air inlet cover and the air outlet cover are both detachable covers, so that the honeycomb activated carbon module 4 is convenient to maintain, assemble and disassemble; the outer alloy wrapping 2 comprises a heating area side detachable outer cover which is mainly used for detaching and maintaining the built-in heating device 5.
The upper layer horizontal support frame of the internal support frame 3 mainly bears the activated carbon module 4, the lower layer horizontal support frame mainly bears the built-in electric heating device 5, the vertical support frame keeps the support system firmer on one hand, and the vertical support frame is a thin plate-shaped framework on the other hand, can play an isolation role in each layer of activated carbon bed layer, and is in an open state at the gas redistribution area 6, so that the gas can be remixed to realize redistribution;
preferably, the honeycomb activated carbon modules 4 are an upper layer and a lower layer which are separated by a built-in heating device 5, 3 areas are arranged in each layer, and each area is provided with 3-4 grade carbon modules.
Preferably, the built-in heating device 5 comprises an electric heating sleeve, a heat transfer plate, a temperature controller 13 at the end A, a thermal desorption valve 12 and sealing covers at the two ends A and B, and is used for generating hot air and controlling the temperature, so that desorption operation is carried out on the honeycomb activated carbon bed layer with saturated adsorption, the concentration of organic matters in the waste gas after desorption is concentrated and higher, and combustion treatment can be carried out after the waste gas is pumped and exhausted through an exhaust valve;
the gas redistribution area 6 is arranged behind each stage of honeycomb activated carbon module 4, a length space of 5-10cm is reserved in each layer of gas redistribution area, a perforated guide plate is arranged in the space, the middle aperture of the perforated guide plate is small, the peripheral aperture of the perforated guide plate is relatively large, and the aperture deviation rate is less than 15%, so that the phenomena of high central gas flow rate and gas concentration are overcome, gas can temporarily stay in the space, the gas remixing of each layer of honeycomb activated carbon is realized, the redistribution work after uniform mixing is realized, the dead angle phenomenon in the area is reduced, the utilization rate of the next layer of activated carbon can be improved, the adsorption efficiency is improved, the early saturation of the activated carbon is delayed, and the organic waste gas is favorably and efficiently treated;
when the on-line monitoring probe 7 works, the control system sends an instruction by detecting whether the purified waste gas meets the standard requirement, switches A, B valves at two ends, and switches adsorption and desorption of an activated carbon bed layer to work alternately, so that continuous operation is realized; the control system 8 sends out an instruction, when the upper activated carbon layer is saturated in adsorption, the first air inlet valve 11 closes the first air outlet valve 16, the heating system is started, when the set desorption temperature is reached, the first thermal desorption valve is opened, meanwhile, the first combustion air inlet valve 24 is opened, and after the second fan 21 is started, the air enters the combustion device 10 to be purified and then is discharged outside; meanwhile, the lower-layer activated carbon adsorption system is started, the second air inlet valve 12 of the other branch is opened, the second air outlet valve 17 is opened, and the first combustion air inlet valve 25 is in a closed state; the above operations are repeated to achieve the purpose of continuous operation.
The utility model discloses a device of desorption organic waste gas is adsorbed in succession in built-in heating integration is equipped with built-in inclosed heating device dismantled all around simultaneously, has both dismantled the maintenance and has maintained the convenience, avoids gaseous short circuit, the entering heating region that leaks at active carbon propulsion in-process again, and whole device has advantages such as heat transfer efficiency is high, quick detachable, desorption effect is good.
The above description is only a preferred example of the present invention, and should not be taken as limiting the invention, and any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention should be included in the scope of the present invention. It should be noted that the features of the embodiments in the present application may be combined with each other without conflict.

Claims (7)

1. A built-in heating integrated device for continuously adsorbing and desorbing organic waste gas is characterized by comprising an alloy outer wrapping body, an inner supporting frame, a honeycomb activated carbon module, a built-in electric heating device, a gas redistribution area, an online monitoring probe, a control system, a fan, an air inlet cover, an air outlet cover, an exhaust funnel and a combustion device; wherein the content of the first and second substances,
the alloy outer wrapping layer is arranged on the outermost layer of the adsorption device;
the internal support frame is arranged in the whole device;
the built-in electric heating device comprises an electric heating sleeve, a heat transfer plate, a temperature controller at the end A, a thermal desorption valve and heating sleeve sealing covers at the two ends A and B;
the honeycomb activated carbon module is arranged around the heat transfer plate and the electric heating sleeve, the electric heating sleeve is arranged at the center, and the heat transfer plate is arranged at the center or the gas redistribution area;
the electric heating sleeve is arranged on the innermost layer of the whole device;
the heat transfer plate is arranged between the internal support frame and the electric heating sleeve;
the gas redistribution area is arranged at the tail end of each stage of honeycomb activated carbon;
the online monitoring probe is arranged at the tail end of the last stage of honeycomb activated carbon;
the control system is an external system and is used for controlling the temperature controller and the online monitoring probe;
the fan is arranged at one end of the honeycomb activated carbon adsorption device;
the honeycomb activated carbon module is an upper layer and a lower layer which are separated by a built-in electric heating device, each layer is provided with 3 areas, and each area is provided with a 3-4-level honeycomb activated carbon module.
2. The device for continuously adsorbing and desorbing organic waste gas with built-in heating integration according to claim 1, wherein: the alloy outer wrapping comprises an A-end air inlet cover, a B-end air outlet cover and a heating area side surface detachable outer cover.
3. The device for continuously adsorbing and desorbing organic waste gas with built-in heating integration according to claim 1, wherein: the inner support frame and the alloy outer wrapping are welded into a whole.
4. The device for continuously adsorbing and desorbing organic waste gas with built-in heating integration according to claim 1, wherein: the honeycomb activated carbon module comprises three to four layers of honeycomb activated carbon beds which are sequentially laid on the internal support frame.
5. The device for continuously adsorbing and desorbing organic waste gas with built-in heating integration according to claim 1, wherein: the electric heating sleeve is placed on the internal support frame through the heat transfer plate, is not fixed and is convenient to take out and maintain at the later stage, and the interior of the electric heating sleeve is hollow to form hot air; two ends of the electric heating sleeve are provided with heating closed covers.
6. The device for continuously adsorbing and desorbing organic waste gas with built-in heating integration according to claim 1, wherein: the heat transfer plate and the internal support frame are not fixed, so that the heat transfer plate is convenient to take out and maintain at the later stage and is directly connected with the electric heating sleeve to obtain heat; and heating sleeve sealing covers are arranged at two ends of the electric heating sleeve.
7. The device for continuously adsorbing and desorbing organic waste gas with built-in heating integration according to claim 1, wherein: the gas redistribution area comprises three to four layers of gas redistribution areas, and a length space of 5-10cm is reserved in each layer of gas redistribution area, so that gas is uniformly mixed again at the position and then enters the next layer of activated carbon for adsorption and purification, the utilization rate of the next layer of activated carbon can be improved, the adsorption efficiency is improved, and the early saturation of the activated carbon is delayed.
CN202022163471.8U 2020-09-28 2020-09-28 Built-in heating integrated device for continuously adsorbing and desorbing organic waste gas Expired - Fee Related CN214914693U (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CN202022163471.8U CN214914693U (en) 2020-09-28 2020-09-28 Built-in heating integrated device for continuously adsorbing and desorbing organic waste gas

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CN202022163471.8U CN214914693U (en) 2020-09-28 2020-09-28 Built-in heating integrated device for continuously adsorbing and desorbing organic waste gas

Publications (1)

Publication Number Publication Date
CN214914693U true CN214914693U (en) 2021-11-30

Family

ID=79034557

Family Applications (1)

Application Number Title Priority Date Filing Date
CN202022163471.8U Expired - Fee Related CN214914693U (en) 2020-09-28 2020-09-28 Built-in heating integrated device for continuously adsorbing and desorbing organic waste gas

Country Status (1)

Country Link
CN (1) CN214914693U (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN112237824A (en) * 2020-09-28 2021-01-19 河南省地质测绘总院 Built-in heating integrated device for continuously adsorbing and desorbing organic waste gas

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN112237824A (en) * 2020-09-28 2021-01-19 河南省地质测绘总院 Built-in heating integrated device for continuously adsorbing and desorbing organic waste gas
CN112237824B (en) * 2020-09-28 2022-05-20 河南省地质测绘总院 Device for continuously adsorbing and desorbing organic waste gas through built-in heating integration

Similar Documents

Publication Publication Date Title
US5198001A (en) Apparatus and process for removing organic compounds from a gas stream
KR100578106B1 (en) Adsorption/catalyst-oxidation VOC removing system for low-concentration VOC disposal
JP2022539398A (en) Parallel piping type gas adsorption concentrator
CN214914693U (en) Built-in heating integrated device for continuously adsorbing and desorbing organic waste gas
CN112237824B (en) Device for continuously adsorbing and desorbing organic waste gas through built-in heating integration
WO2022104252A1 (en) An improved system for direct air capture of carbon dioxide without movement
JP2007000733A5 (en)
JP5109028B2 (en) Method for purifying a large amount of exhaust gas containing lean volatile hydrocarbons
CN110935281B (en) Adsorption and regeneration device and method for solid adsorbent for adsorbing volatile organic compounds
CN209885575U (en) Paint spraying waste gas adsorption, desorption and catalysis integrated device
CN216431760U (en) Activated carbon adsorption desorption catalytic combustion equipment
JPH10337438A (en) Mobile cell type adsorption desorption device and its use method
JP2011072919A (en) System for treating gas containing organic solvent
CN210125299U (en) Organic waste gas concentration catalytic treatment system
JP5441485B2 (en) Volatile organic substance processing apparatus and volatile organic substance processing method
KR102518395B1 (en) Apparatus for removing VOCs
CN113209773A (en) VOCs adsorption and desorption equipment and method
CN111701393A (en) Adsorption equipment with axial radial adsorption and treatment system for industrial waste gas
CN110624360A (en) VOCs waste gas purification device, purification method and purification system
CN205730780U (en) Organic exhaust gas purifying system based on zeolite adsorption desorption
WO2023042302A1 (en) Ethylene oxide gas removal method, and ethylene oxide gas removal system using same
CN208771123U (en) A kind of industrial waste gas processing equipment using absorption and catalytic way
CN219002518U (en) Waste gas purifying device adopting granular adsorbent
CN210385340U (en) Device for treating organic waste gas
JPH05123525A (en) Gas purifying method and apparatus therefor

Legal Events

Date Code Title Description
GR01 Patent grant
GR01 Patent grant
CF01 Termination of patent right due to non-payment of annual fee

Granted publication date: 20211130

CF01 Termination of patent right due to non-payment of annual fee