CN111854373A

CN111854373A - Ammonium chloride closed cycle drying system and process

Info

Publication number: CN111854373A
Application number: CN202010728942.7A
Authority: CN
Inventors: 王宏耀; 蒋斌; 张海滨; 尹凤交; 史元芝; 王宗辉
Original assignee: Shandong Tianli Energy Co ltd
Current assignee: SHANDONG TIANLI ENERGY Co.,Ltd.; China Chengda Engineering Co Ltd
Priority date: 2020-07-27
Filing date: 2020-07-27
Publication date: 2020-10-30

Abstract

In the embodiment of the invention, the tail gas is further dehumidified after being purified and then used as moisture carrying gas for recycling, so that the direct exhaust amount of the tail gas is reduced, and the pollution to the environment is reduced.

Description

Ammonium chloride closed cycle drying system and process

Technical Field

The invention relates to an ammonium chloride closed cycle drying system and also relates to an ammonium chloride closed cycle drying process.

Background

Ammonium chloride is colorless crystal or white crystalline powder, and has hygroscopicity. The powdery ammonium chloride is extremely easy to deliquesce, and the moisture absorption point is about 76 percent generally. When the relative humidity in the air is higher than the moisture absorption point, the ammonium chloride generates the moisture absorption phenomenon, and is easy to agglomerate, thereby influencing the use of the ammonium chloride. Therefore, drying of the ammonium chloride is required before packaging to avoid caking.

Currently, the main industrial source of ammonium chloride is the combined soda process. Ammonia gas is one of main raw materials of the combined alkali method, and a certain amount of ammonia water or ammonium carbonate is carried in the produced ammonium chloride. After heating, both readily decompose to produce free ammonia. Therefore, when the ammonium chloride is dried, ammonia gas is generated by volatilization, and the environment is polluted.

In addition, ammonium chloride is relatively weak in chemical stability and starts to decompose at 100 ℃ and can be completely decomposed into ammonia gas and hydrogen chloride gas at 337.8 ℃. Therefore, the drying temperature is not necessarily too high when drying ammonium chloride.

It is to be noted that in the field of material drying, the material before drying is generally referred to as wet material, as indicated by reference numeral 3 in fig. 1; the dried material is generally referred to as a dry material, such as a dry product, as indicated by reference numeral 16 in fig. 1. It is to be understood that dry and wet materials are collectively referred to as materials. In the drying process, the gas used to carry away the components volatilized from the drying, such as water vapor, ammonia gas, ammonium chloride dust, is generally referred to as moisture-laden. Moisture-laden air is used as a working gas during the drying process.

Fig. 1 shows a schematic diagram of a known internal heating fluidized bed drying system, which is also a conventional ammonium chloride drying system. In the figure, the fluidized bed 4 is configured such that the heating air for drying the material is supplied to the front stage by the drying blower 23 and the cooling air for cooling the material is supplied to the rear stage by the cooling blower 24. The heated air and the cooling air are used as functional gases for heating or cooling materials and are used as moisture-carrying gases, and the gases are used as dry tail gas, subjected to two-stage dust removal by the cyclone dust collector 6 and the bag-type dust collector 9, subjected to ammonia removal by the wet dust collector and directly discharged into the atmosphere 11. In contrast, the functional gas is used as a carrier gas, which is in serious excess in terms of the requirement of carrying moisture, and is easy to carry away a larger amount of ammonia gas and hydrogen chloride gas generated by heating, which inevitably increases the difficulty of dry tail gas treatment. And because of containing more harmful gases, the cleaning is difficult and the environmental pollution is easy to cause.

In addition, the drying tail gas often takes away more heat, which results in higher overall drying energy consumption. Meanwhile, once the types of the fluidized bed 4 and the airflow dryer are determined, the fluidization wind speed and the air inlet temperature are not allowed to fluctuate greatly due to the characteristics of fluidization drying of the materials, the air inlet amount and the energy consumption are determined, and the elasticity of the product is small. Meanwhile, the ammonium chloride particles are in a fluid state by fluidization through airflow, are in a turbulent flow state, are easy to generate violent collision with drying and circulating process equipment, damage crystal forms and generate fine dust materials, so that the particle size distribution of the ammonium chloride is poor, and the dust materials are easy to be carried out by dry tail gas to generate loss.

Chinese patent document CN207849900U discloses a closed-cycle fluidization system for ammonium chloride drying, which employs two fluidized beds 4, one of which is configured as a fluidized bed dryer and the other of which is configured as a fluidized bed cooler, and uses carbon dioxide as a moisture-carrying and heated working gas. Most of the working gas is recycled after cloth bag dust removal and water washing deamination. The carbon dioxide can be combined with ammonia gas to generate ammonium carbonate, and the content of the ammonia gas in the working gas can be reduced. However, the dual-purpose of the working gas is an inherent characteristic of the fluidized bed, the problem of large amount of dry tail gas cannot be solved all the time, and even if the internal circulation is adopted, the environmental friendliness is good, but the workload of the process equipment for removing ammonia gas is increased. Meanwhile, the problems that the ammonium chloride has poor particle size distribution and more materials are carried away by working tail gas cannot be avoided. In particular, the carbon dioxide needs to be supplied continuously, so that the problem of 'cycle gas expansion' is easily caused in a process system, and accidents are easily caused when the load of process equipment is exceeded.

Chinese patent document CN208419545U discloses a steam rotary drying system for ammonium salts, in which the moisture-carrying gas is independently distributed, and the water vapor for heating is not in direct contact with the material, but exchanges heat by means of physical isolation. The carrying capacity of the moisture-carrying ammonia gas and dust can be greatly reduced due to the small amount of the moisture-carrying gas and the slow flow rate. This patent document relies on a rotary drum in which a conduit for the circulation of saturated steam is mounted, the material being moved gradually from one end of the inclined rotary drum to the other while being turned over as the rotary drum rotates. And the rotating speed of the rotary drum is relatively low, so that ammonium chloride particles are not easy to break or wear, and the particle size distribution of the ammonium chloride is better. In addition to the slower velocity of the moisture laden air, the amount of ammonium chloride particles that can be entrained by the moisture laden air is relatively small. However, in the patent document, an open-circuit type tail gas system is adopted for the dry tail gas, the tail gas is directly exhausted after being treated, and the tail gas is difficult to reach the emission standard even though being treated. In addition, the cooling still requires more cold air as cooling air and fluidizing air, still causes greater consumption of working gas, and increases the burden of the subsequent treatment. At the same time, the presence of a fluidized bed also limits its operating flexibility, increasing the energy consumption in low-energy production.

Disclosure of Invention

The invention aims to provide an ammonium chloride closed cycle drying system capable of effectively reducing tail gas emission and also provides an ammonium chloride closed cycle drying process.

In an embodiment of the present invention, there is provided an ammonium chloride drying system comprising:

one end of the steam rotary dryer is a feeding end, and the other end of the steam rotary dryer is a discharging end;

the moisture-carrying assembly is connected into the steam rotary dryer from the feed end;

a feed assembly for introducing wet material into the steam rotary dryer at a feed end;

the discharging assembly is used for guiding the dry materials out of the steam rotary dryer from the discharging end;

the tail gas closed circulation system is used for guiding out moisture-carrying gas from the discharge end and purifying the moisture-carrying gas; the tail gas closed circulation system comprises a first branch which is connected to the moisture-carrying assembly in a return mode and at least provided with a demister.

Optionally, the first branch is provided with a cooling device at a preceding stage of the demister.

Optionally, the moisture-laden assembly includes an air preheater for preheating the moisture-laden air prior to introduction into the steam rotary dryer.

Optionally, the moisture-carrying assembly includes an air supply branch;

the tail gas closed-loop circulating system comprises a second branch, and the second branch is used for discharging the purified part of moisture-carrying gas into the atmosphere.

Optionally, the discharge assembly is provided with a cooler;

the cooler is provided with a loosening air device which comprises a compressed air system;

a chamber of the cooler for circulating the dry materials is provided with a loosening air hole or an aeration head;

and the loose air holes or the aeration heads are connected with the compressed air system.

Optionally, an exhaust port is arranged on the cooler, and the exhaust port is connected to the tail gas closed cycle system.

Optionally, the tail gas closed cycle system comprises a cyclone dust collector positioned at the front stage and a wet dust collector positioned at the rear stage;

wherein the wet dust collector is based on spraying;

correspondingly, a circulating pipeline and a matched spray pump are provided for circulating spray water; the circulating pipeline is provided with a bypass for discharging concentrated liquid, and the wet dust collector is provided with a liquid supplementing branch for supplementing liquid.

In an embodiment of the present invention, there is also provided a closed cycle drying method of ammonium chloride, comprising the steps of:

1) drying the introduced wet material by using a steam rotary dryer, and introducing moisture from the feed end of the steam rotary dryer in the drying process;

2) the moisture-carrying gas is led out from the discharge end of the steam rotary dryer;

3) purifying the discharged moisture-carrying gas;

4) dehumidifying the purified moisture-carrying gas;

5) and introducing all or part of the dehumidified moisture-carrying gas into the steam rotary dryer.

Optionally, the moisture-laden air is cooled in step 4) before being dehumidified.

Optionally, before the moisture-carrying gas is introduced into the steam rotary dryer, the moisture-carrying gas is heated to reach a temperature of 130-160 ℃.

Optionally, before the purified moisture-carrying gas is introduced into the steam rotary dryer, if the gas supply amount or the gas supply pressure is insufficient, the gas supply amount or the gas supply pressure is balanced in a gas supply manner;

if the gas supply amount or the gas supply pressure before gas supply exceeds a set value, balancing the gas supply amount or the gas supply pressure in a discharging mode;

the discharge point is located before the equipment for dehumidification in step 4).

Alternatively, the compressed air used to tumble the dry material is collected into an off-gas closed cycle system after tumbling the dry material to incorporate the moisture laden.

Alternatively, the moisture-laden air purification method is to first perform cyclone dust removal and then perform spray washing.

Optionally, the washing liquid of the spray washing is used based on an internal circulation mode or a mode of discharging after spraying;

if the internal circulation mode is adopted, concentrated solution with the concentration reaching the given requirement is discharged at regular time, and then diluted solution is supplemented.

Optionally, the weak solution is softened water or a filtration mother liquor of ammonium chloride;

when the filtered mother liquor is used as the washing liquid, the mother liquor is discharged after being sprayed.

In the embodiment of the invention, the tail gas is further dehumidified after being purified and then used as moisture-carrying gas for recycling, so that the direct exhaust amount of the tail gas is reduced, and the pollution to the environment is reduced.

Drawings

Fig. 1 is a schematic diagram of a known internal heating fluidized bed drying system.

FIG. 2 is a schematic diagram of a closed-loop drying system for ammonium chloride in the first embodiment.

FIG. 3 is a schematic diagram of a closed cycle drying system for ammonium chloride in comparison with the first embodiment.

FIG. 4 is a schematic diagram of a closed-loop drying system for ammonium chloride in a second embodiment.

FIG. 5 is a schematic diagram of an ammonium chloride drying system in comparison with a second embodiment.

FIG. 6 is a schematic diagram of an exemplary embodiment of an end of a steam rotary dryer.

FIG. 7 is a schematic cross-sectional view of the middle portion of the steam rotary dryer in one embodiment.

Fig. 8 is a schematic diagram of a first striker plate structure in an embodiment.

Fig. 9 is a schematic structural diagram of a second retainer plate in an embodiment.

In the figure: 1. condensed water discharge, 2 saturated steam, 3 wet materials, 4 fluidized bed, 5 returning material screw conveyer, 6 cyclone dust collector, 7 cyclone discharge valve, 8 returning material discharge valve, 9 bag dust collector, 10 induced draft fan, 11 exhaust into atmosphere, 12 wet dust collector, 13 screw conveyer, 14 bag discharge valve, 15 spray water pump, 16 drying product, 17 circulating water return, 18 circulating water upper water, 19 bucket elevator, 20 vibrating screen, 21 discharging discharge valve, 22 air preheater, 23 drying blower, 24 cooling blower, 25 blower, 26 zero pressure point, 27 demister, 28 surface cooler, 29 induced draft fan, 30 soft water supplement, 31 concentrated liquid discharge, 32 product discharge valve, 33 powder flow cooler, 34 star discharge valve, 35 discharging screw conveyer, 36. the device comprises a discharge cover, 37 parts of a steam rotary dryer, 38 parts of a mixer, 39 parts of a washing cooler, 40 parts of a seat, 41 parts of a pipe through hole, 42 parts of a discharge end plate, 43 parts of a discharge hole, 44 parts of a cover plate, 45 parts of a discharge hole, 46 parts of a pipe support body, 47 parts of a first baffle plate, 48 parts of a second baffle plate, 49 parts of a pipe support groove, 50 parts of an assembly hole, 51 parts of a plate body, 52 parts of an assembly hole and 53 parts of the plate body.

Detailed Description

It will be appreciated that the gas discharged directly into the atmosphere by a system may be referred to as tail gas. Correspondingly, the working gas is recycled in the system and can be called as working gas. In the embodiment of the present invention, the working gas for carrying away moisture generated in the drying process or gas which can be carried away with the air flow, ammonium chloride dust, and the like is referred to as moisture-carrying gas. For convenience of description, unless otherwise specified, the working gas in a circulating state for carrying moisture or other harmful gases generated during the drying process is collectively referred to as moisture-carrying gas. Moisture-laden air in the cycle phase can be referred to as cycle moisture-laden air.

For the purpose of distinction, the moisture-laden air is referred to as tail gas from the stage after the moisture-laden air is discharged from the steam rotary dryer 37 to the stage before the process purification because the moisture-laden air changes its composition after being discharged from the steam rotary dryer 37. It follows that under the conditions defined herein, an exhaust gas is a term for carrying moisture at a certain stage.

For further differentiation, in the drying process, the moisture-laden air of the leaking part is called leaking moisture-laden air, and the purge of off-gas discharged into the atmosphere 11 part is called evacuation off-gas.

In the embodiment of the present invention, the core processing equipment is the steam rotary dryer 37, and the steam rotary dryer 37 disclosed in chinese patent documents CN 204944086U, CN 204757589U, CN201014901Y, CN201377966Y, CN 201575669U, etc. can be selected. Such a steam rotary dryer 37 is distinguished from a conventional dryer in that the medium that supplies thermal energy for drying is saturated steam. The heat exchange adopts indirect mode to realize, does not produce direct contact between heating medium and material, and generally speaking, the heat exchange tube is through arranging in steam rotary dryer 37, and saturated steam circulates in the heat exchange tube, and the material is along axial displacement in steam rotary dryer 37's a revolving drum, and the material can be stirred to rotatory revolving drum simultaneously to realize indirect drying.

Further, a separate moisture carrying assembly is provided, moisture carrying is circulated from one end of the rotary drum to the other end, and a relatively small amount of moisture is required.

In general, the rotary drum of the steam rotary dryer 37 is of a typical cylindrical structure, but has one end and the other end defined, and in general, the material is fed from one end and discharged from the other end. One end for feeding is marked as a feeding end, and one end for discharging is marked as a discharging end.

The rotary drum of the steam rotary dryer 37 has an installation inclination angle of 1.5-3.5 degrees from the feed end to the discharge end, and the discharge end is lower than the feed end. When the rotary drum is in a working state, the rotary drum rotates at the rotating speed of 2-5 rpm, and materials move from the feeding side to the discharging side along with the rotation of the rotary drum. In the steam rotary dryer 37, the material is indirectly contacted with the heating steam, the temperature is gradually increased for dehydration, and the evaporated moisture is taken away by the moisture-carrying gas. The retention time of the materials in the dryer is 15-25 min, so that sufficient drying is achieved. The dried material is discharged from the bottom of the discharging cover 36, and is conveyed and lifted by the discharging screw conveyor 35, the star-shaped discharging valve 34 and the bucket elevator 19. The dried product is screened by a vibrating screen 20 to remove lumps. Most of the sieved powder is cooled by a powder flow cooler 33 and discharged by a product discharge valve 32 to obtain a dry product.

The steam rotary dryer 37 generally uses saturated steam with the pressure of 0.35-1.6 MPa as a drying heat source and is connected to a heat exchange tube assembly in a rotary cylinder of the steam rotary dryer 37 through rotary sealing.

In the embodiment of the present invention, the moisture-laden air assembly is pumped into the original moisture-laden air from the feed end into the steam rotary dryer 37 using, for example, a blower 25 in fig. 2 and 4. The moisture-laden air pumped in from the blower 25 is a narrow moisture-laden air, and in addition to the narrow moisture-laden air, a narrow portion of the moisture-laden air is circulated back to the steam-swing dryer 37 during normal operation of the steam-swing dryer 37.

Further, recycling means that other substances carried in the laden moisture, such as water vapor, ammonia, and dust, must be disposed of. Therefore, an exhaust gas closed circulation system is provided, and the exhaust gas closed circulation system leads out moisture-carrying gas from the discharge end and purifies the moisture-carrying gas; the exhaust closed cycle system includes a first branch that is looped back to the moisture-laden assembly. Since conventional purification also includes wet purification, the purified moisture-laden air tends to have a high water content, for which purpose the first branch is provided with at least a demister 27 to improve the moisture-carrying capacity of the recirculated moisture-laden air.

In fig. 2 and 4, the front end of the discharge cover 36 fixedly arranged is in dynamic sealing fit with the rotary drum, and the tail gas closed circulation system is connected out from the top of the discharge cover 36, so that tail gas on the side of the rotary drum can be sucked and discharged by adopting an induced air mode.

In fig. 2 and 4, the exhaust gas closed-loop circulation system comprises two stages of purification, it being apparent that the art concerning purification of exhaust gas comprises at least one stage, generally no more than four stages, with relatively many two stages and three stages.

The first-stage purification device is a cyclone dust collector 6, working media such as filtering and spraying are not needed for dust removal of the cyclone dust collector 6, dust particles are separated from tail gas by means of centrifugal force, the dust particles are settled, and settled materials can be recovered.

The lower part of the cyclone dust collector 6 consists of an ash bucket and a cyclone discharge valve 7 arranged at the lower end of the ash bucket, and materials can be recovered through the cyclone discharge valve 7.

The induced draft fan 29 in fig. 2 and 4 is used for extracting the tail gas in the discharging cover 36 in an induced draft mode, and the leakage of the tail gas at the matching part of the discharging cover 36 and the rotary drum is reduced.

The gas discharged from the induced draft fan 29 is sent to the wet dust collector 12 shown in fig. 2 and 4, and the ammonia gas, the hydrogen chloride and the finer dust in the tail gas are dissolved or settled down by means of spraying.

Conventionally, as shown in fig. 3 and 5, the exhaust gas purified by the exhaust gas purification system is generally directly discharged into the atmosphere, while in the structure shown in fig. 2 and 4, the purified exhaust gas is returned to the moisture-carrying assembly by demisting to reduce the amount of exhaust gas discharged.

In addition, as a basic configuration, the ammonium chloride drying system further comprises a feed assembly for introducing wet material into the steam rotary dryer at a feed end and a discharge assembly for discharging dry material from the discharge end.

In fig. 2 and 4, the feed assembly employs a blender 38 for mixing wet material and partially dry material and feeding the mixture to a steam rotary dryer 37. If the dry materials are not mixed, they may be fed to the steam rotary dryer 37 using, for example, a screw conveyor, or other conveying mechanism.

Feeding using a screw conveyor is that the screw conveyor has a cylindrical housing which facilitates a relatively good seal with the steam rotary dryer 37.

The discharging assembly is in the structure shown in fig. 2 and 4, is adapted to the lower end of the discharging cover 36, and is provided with a discharging screw conveyor 35, and further provided with a star-shaped discharging valve 34, a bucket elevator 19 for elevating the dry material to a given height, a vibrating screen 20 for receiving the bucket elevator 19, and a powder flow cooler 33 for receiving the material screened by the vibrating screen 20, wherein the lower end of the powder flow cooler 33 is provided with a product discharging valve 32 for discharging the finished product.

The steam rotary dryer 37 can be adjusted in its output by changing the rotational speed relative to the fluidized bed 4, and the flow rate can be adapted accordingly.

In the structures shown in fig. 2 and 4, a cooling device is arranged on the first branch at the front stage of the demister 27, such as the surface air cooler 28 shown in the drawings, the surface air cooler 28 may be an air heat exchanger or a liquid cooling heat exchanger, and if the surface air cooler is an air heat exchanger, the cooling fan can be adapted to enhance the cooling effect of the surface air cooler 28.

It is understood that the heat exchanger is one of the most basic cooling or heating devices, and any cooling device for cooling the purified exhaust gas based on heat exchange can be applied to the present application, such as a shell-and-tube heat exchanger.

The cooling of the purified tail gas, the moisture carrying capacity of which is reduced, contributes to improving the demisting rate of the demister 27, or reduces the moisture content of the moisture-carrying gas, thereby improving the moisture carrying capacity of the moisture-carrying gas.

The improvement in moisture carrying capacity may also be enhanced in some embodiments by increasing the temperature of the moisture carrying gas, and therefore the moisture carrying gas assembly includes an air preheater 22 for preheating the moisture carrying gas prior to introduction into the steam rotary dryer 37. The preheating of the moisture-carrying substances is required to be 110-160 ℃ in a preferred embodiment.

The cartridge of the blender 38 in fig. 2 may have an air inlet to which the air preheater 22 is connected by piping to introduce moisture-laden air.

The introduction of preheated moisture-laden air at mixer 38 helps to quickly carry away some of the water vapor and reduce the likelihood of binding of the wet material during transport. The method has the advantages that moisture is carried through preheating, so that the temperature of the moisture is increased, the drying efficiency of the material at the feeding section is improved, the wet material is dehydrated as soon as possible, and the viscosity is reduced.

The preheated moisture-carrying gas comprises moisture-carrying gas directly pumped in by the blower 25 and circulating moisture-carrying gas, the latter is the moisture-carrying gas generated after tail gas purification by cooling and demisting, the circulating moisture-carrying gas is introduced into the drying process of the material by circulation, the discharge amount of the tail gas can be greatly reduced, the discharge of ammonia gas and dust is reduced, and environment-friendly production is realized.

In the steam rotary dryer 37 shown in fig. 3 and 5, the same material is dried by 100-120 m per ton³The amount of exhaust gas discharged; for the traditional fluidized bed drying, the thickness is 800-1000 m³Tail gas/ton handling capacity; according to the ammonium chloride drying system based on the embodiment of the invention, the moisture-carrying gas is recycled, so that the exhaust emission can be reduced to 10-15 m³The treatment capacity per ton of tail gas and the discharge amount are approximately equivalent to the air leakage amount of equipment.

In addition to air as the moisture carrier, compressed air, nitrogen, carbon dioxide, or the like may be used as the moisture carrier.

For the tail gas exhausted into the atmosphere 11, the ammonia concentration before tail gas treatment is 950-5000 mg/m³The concentration of the ammonia after dust removal and ammonia removal is 53-66 mg/m³The net emission of ammonia is in direct proportion to the emission of tail gas, and the net emission of ammonia can be greatly reduced according to the calculation of the same emission concentration because the emission of tail gas is reduced.

Further, the moisture-carrying assembly comprises an air supply branch;

In the configuration shown in fig. 2 and 4, the wet scrubber 12 is provided with an exhaust bypass, i.e., a bypass to the atmosphere 11, at a later stage. According to the process requirement, a small amount of tail gas can be discharged through a bypass, and the rest tail gas is used as circulating moisture-carrying gas. In order to maintain the moisture carrying capacity of the circulating moisture-carrying agent, the circulating moisture-carrying agent is first cooled by the surface air cooler 28, and the circulating moisture-carrying agent is cooled by using chilled water as a cooling medium for rapid cooling. The water vapor in the circulating moisture-carrying gas is condensed and dewed, and is discharged outside through a water discharge port of the surface air cooler 28. And then the entrained liquid drops are removed by the demister 27, so that the water content in the circulating moisture-carrying gas is reduced, and the requirement of the circulating moisture-carrying gas is met.

Moisture-carrying gas lost during the drying process is replenished by a separately provided blower 25.

Fig. 2 and 4 respectively show a material returning mode, fig. 2 shows an external circulation material returning structure, fig. 4 shows a self-returning material of a rotary drum, and the returning of partial dry materials can solve the problems of wall sticking, caking and low thermal efficiency of wet materials. The rotary drum can simplify the material returning equipment by self material returning, and the occupied area of the equipment is reduced.

The rotary drum realizes the returning charge from the returning charge through the mode of constructing the returning charge structure on the outer surface of the rotary drum, specifically, a spiral returning charge channel is arranged on the outer surface of the rotary drum, and a small amount of dry materials can return to the feeding end through the returning charge channel in the rotating process of the rotary drum through the adaptation of turning.

The material returning mechanism can be seen from the structure shown in fig. 2, an independent conveying mechanism needs to be provided, and the occupied area is relatively large. In fig. 2, the return mechanism is configured as a return screw conveyor 5.

The material returning positions of the two material returning modes are different, in fig. 2, the material returning position is taken from the dry material sieved by the vibrating screen 20, and in the structure shown in fig. 4, the material returning position is the discharging end of the rotary drum.

The dry material and the wet material of this given volume are mixed the back and are fed to steam rotary dryer 37, can effectively avoid the material to glue the pipe, glue the wall problem, improve production stability.

Because of the difference of wet material water content, and the behavior can change in the course of the work, for the convenient suitable material returning ratio of adjustment, material returning mechanism and feed back passageway all are equipped with flow control device.

The simplest control method for flow control is through a flow control valve.

In the configuration shown in fig. 2 and 4, the discharge assembly is provided with a powder flow cooler 33 to cool the dried dry material, and then package the material.

The powder flow cooler 33 is equipped with a loosening air device comprising a compressed air system;

the powder flow cooler 33 is provided with loose air holes or an aeration head in a cavity for circulating dry materials;

The loose air is discharged inevitably, the dried dry materials still maintain a certain temperature, the ammonia gas still volatilizes, the loose air forms another type of moisture-carrying gas, and therefore the air discharged from the powder flow cooler 13 is guided into the tail gas closed circulation system to be purified together with the tail gas directly discharged from the steam rotary dryer 37. Solves the secondary pollution problem of 'gas stripping ammonia removal' and the problem of 'circulating gas expansion'.

When the powder flow is cooled, the loose air volume is far less than the dry air volume, and the powder flow cooler exhausts air in positive pressure, so that the air is easy to distribute, and the operation and the adjustment are simple.

In the preferred embodiment, the drying capacity of the steam rotary dryer 37 increases from the feed end to the discharge end. Aiming at the material characteristics, the rotary cylinder is axially divided into a feeding section and a drying section, and the intervals of the annular heat exchange tubes at different positions are different. The feeding section is located the feed end of rotary drum, and its length is 1.5~3m, and the centre-to-centre spacing of its annular heat exchange tube is 150~300 mm. The drying section is located between the feeding section and the discharging cover 36, and the center distance of the annular heat exchange tubes is 100-130 mm. The feeding adopts larger space, which can prevent the wet material from adhering between the heat exchange tubes. The drying section adopts smaller space, can improve effective heat exchange area, increases the barrel utilization ratio.

Fig. 6 shows a schematic structural view of the tail end, i.e., the discharge end, of the rotary drum of the steam rotary dryer 37, in which the discharge end is blocked by an end plate to form a discharge end plate 42 shown in the figure, and the discharge end plate 42 is provided with a discharge opening, i.e., a discharge opening 43 shown in fig. 6.

The flash port is provided with an adjusting mechanism for adjusting the opening degree of the flash port, so that the opening degree of the discharge port 43 is changed by adjusting the adjusting mechanism, and the layer thickness of the material in the rotary cylinder is changed to adapt to different applications.

In the structure shown in fig. 6, the adjustment mechanism is configured to:

the two opposite sides of the flash opening are provided with slots for providing insertion plates guiding the slots so as to adjust the opening of the flash opening through the positions of the insertion plates in the slots.

In fig. 6, the cover plate 44 is a fixed plate, a plurality of adjusting holes are provided on both sides of the discharge hole 43, and the position of the cover plate 44 is adjusted by assembling on different adjusting holes.

In addition, the edge of the discharging end plate 42 is provided with at least one discharging opening 45 with a sealing door, the sealing door can be normally opened or normally closed, and even if the sealing door is normally opened, the influence on the whole drying stroke is not great. The discharge opening 45 is mainly used for the clean discharge operation of the dry materials before the shutdown.

Fig. 7 is a schematic cross-sectional structure view of the middle of a rotary drum, specifically, at least one and no more than three separation points are arranged in the rotary drum of the steam rotary dryer 37, each separation point is provided with a plurality of baffle plate groups perpendicular to the axis of the rotary drum, and the interior of the rotary drum is divided into a plurality of drying zones;

a pipe support body 46 for supporting the axial pipe of the saturated steam pipe is arranged between the baffle plate groups;

a discharge gap is defined between the baffle group and the pipe support 46 for the material in the front stage drying area to flow to the rear stage drying area.

The retention time of the material in a certain drying area can be prolonged by blocking the material through the material baffle plate group, so that the drying effect is improved.

As for the striker plate group, as shown in fig. 7, it is assembled by a plurality of first striker plates 47 and second striker plates 38.

It should be noted that the tightness of the assembly of the striker plate group is not required to be very high.

The striker plate can be assembled on a pipe shaft at the center of the rotary cylinder or assembled with each other to form an annular structure.

In the configuration shown in fig. 2 and 4, the subsequent purification device for purifying the exhaust gas is a wet dust collector 12, and the wet dust collector 12 is a dust collector for performing dust fall by a spray method. In fig. 1, the part for supplying shower water includes a circulation line and a shower pump equipped, i.e., a shower water pump 15 shown in the drawing, for circulating shower water; the concentration of the spray water is increased gradually by the circulating spray, and for this purpose, the circulating pipeline is provided with a bypass for discharging the concentrated liquid, namely a pipeline corresponding to the concentrated liquid discharge 31 shown in fig. 2 and 4. The wet scrubber 12 is also provided with a fluid replacement branch for replacement fluid, such as the piping for the soft water replacement 30 shown in fig. 2 and 4.

From the above description, the flow of the ammonium chloride drying method is roughly clear, and it includes the following steps:

1) drying the introduced wet material by using a steam rotary dryer 37, and introducing moisture from the feed end of the steam rotary dryer 37 in the drying process;

2) moisture-carrying gas is led out from the discharge end of the steam rotary dryer 37;

3) purifying the discharged moisture-carrying gas;

4) dehumidifying the purified moisture-carrying gas;

5) the dehumidified moisture-laden air is entirely or partially directed to a steam rotary dryer 37.

Furthermore, in step 4), the moisture-laden air is cooled before being dehumidified.

Before the moisture-carrying gas is introduced into the steam rotary dryer 37, the moisture-carrying gas is heated to a temperature of 130 to 160 ℃.

Before the purified moisture-carrying gas is introduced into the steam rotary dryer 37, if the gas supply amount or the gas supply pressure is insufficient, the gas supply amount or the gas supply pressure is balanced in a gas supply manner;

The wet material is mixed with a predetermined amount of dry material before being introduced into the steam rotary dryer 37.

The drying capacity of the material is gradually enhanced in the drying circulation process.

The drying time of the materials is 15-25 min.

Screening the dry materials, and then cooling the screened dry materials;

when the dry materials are cooled, compressed air is introduced to turn over the dry materials to avoid bonding.

The compressed air used to tumble the dry material is collected into an exhaust closed cycle system after tumbling the dry material to incorporate the moisture laden.

The moisture-carrying purifying method is to perform cyclone dust removal and then perform spray washing.

The washing liquid for spraying and washing is used based on an internal circulation mode or a mode of discharging after spraying;

The weak solution is softened water or filtered mother solution of ammonium chloride;

Claims

1. An ammonium chloride closed cycle drying system, comprising:

the tail gas closed circulation system is used for guiding out moisture-carrying gas from the discharge end and purifying the moisture-carrying gas; the tail gas purification system comprises a first branch which is connected to the moisture-carrying assembly in a loop mode, and the first branch is at least provided with a demister.

2. The closed cycle drying system of claim 1, wherein the first branch is provided with a cooling device at a pre-stage of the demister.

3. A closed cycle ammonium chloride drying system as claimed in claim 1 or claim 2 wherein the moisture laden air assembly includes an air preheater for preheating the moisture laden air prior to introduction into the steam rotary dryer.

4. The closed loop drying system of claim 3, wherein the moisture-laden air assembly includes an air make-up branch;

5. The closed cycle drying system of ammonium chloride according to claim 1, wherein the discharge assembly is provided with a cooler;

6. The closed cycle drying system of claim 5, wherein the cooler has an exhaust port connected to the tail gas purification system.

7. The ammonium chloride closed cycle drying system of claim 1, wherein the tail gas closed cycle system comprises a cyclone dust collector at a front stage and a wet dust collector at a rear stage;

wherein the wet dust collector is based on spraying;

8. A closed-loop circulation drying method for ammonium chloride is characterized by comprising the following steps:

3) purifying the discharged moisture-carrying gas;

4) dehumidifying the purified moisture-carrying gas;

9. The closed cycle drying method of ammonium chloride according to claim 8, wherein the moisture-laden gas is cooled before being dehumidified in step 4).

10. The closed cycle drying method of ammonium chloride according to claim 7 or 8, wherein the moisture-laden air is heated to a temperature of 130-160 ℃ before being introduced into the steam rotary dryer.

11. The closed cycle drying method of ammonium chloride according to claim 8, wherein the amount of the feed gas or the feed gas pressure is balanced by the way of the feed gas if the amount of the feed gas or the feed gas pressure is insufficient before the purified moisture-laden gas is introduced into the steam rotary dryer;

12. The closed cycle drying method of ammonium chloride according to claim 8, wherein the dry material is sieved and then cooled;

13. The closed cycle drying method of ammonium chloride according to claim 12, wherein the compressed air used to tumble the dry materials is collected into an exhaust gas purification system after tumbling the dry materials to incorporate moisture.

14. The closed cycle drying method of ammonium chloride according to claim 8, wherein the moisture-laden air is purified by cyclone dust removal and then spray washing.

15. The closed cycle drying method of ammonium chloride according to claim 14, wherein the washing solution of spray washing is used based on an internal circulation mode or a mode of discharging after spraying;

if an internal circulation mode is adopted, concentrated solution with the concentration reaching the given requirement is discharged at regular time, and then diluted solution is supplemented.

16. The closed cycle drying method of ammonium chloride according to claim 15, wherein the weak solution is softened water or filtered mother solution of ammonium chloride;