Method and system for deeply removing volatile substances from synthetic resin

Abstract

The present invention belongs to the technical field of synthetic resins, and discloses a method and a system for deeply removing volatile substances from synthetic resins. The method includes: resin particles enter from the top of a ridge-type devolatilization tower, and successively pass through the first heating section, the second heating section and the cooling section of the ridge-type devolatilization tower from top to bottom, and fall to the bottom of the ridge-type devolatilization tower for discharge; a first mixed gas composed of nitrogen and steam passes through the cooling section and directly contacts and exchanges heat with the resin particles, and then after pressurization, heating and primary steam supplementation, a second mixed gas is obtained; the second mixed gas passes through the second heating section and directly contacts and exchanges heat with the resin particles, and then after pressurization, heating and secondary steam supplementation, a third mixed gas is obtained; the third mixed gas passes through the first heating section and directly contacts and exchanges heat with the resin particles, and then after cooling, the obtained gas is discharged, and the condensate enters the sewage treatment system for treatment. This method has low energy consumption and good devolatilization effect.

Description

Technical Field

[0001] The present invention belongs to the technical field of synthetic resins, and specifically, relates to a method and a system for deeply removing volatile substances from synthetic resins. Background Art

[0002] Synthetic resins such as polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), and polystyrene (PS) are widely used in pipes, interior decoration, household appliances, etc. With the increasing application of synthetic resins in fields such as automobiles and homes, and the improvement of people's awareness of health and environmental protection, more and more attention is paid to the emissions of volatile organic compounds (VOCs) and the odors generated during the processing and use of materials, and the requirements are getting higher and higher. Technologies for reducing the content of volatile substances in synthetic resin materials are the focus of development in the industry.

[0003] The prior art generally uses professional devolatilization equipment to carry out devolatilization during the processing. Patent document CN101255252B discloses that by adding expelling agents such as sodium bicarbonate, magnesium bicarbonate, calcium bicarbonate, water, low-boiling fatty alcohols, etc., the VOC of the material can be reduced. However, it is difficult for the expelling agent to be stably dispersed in the polypropylene melt, and the effective time of the expelling agent in the system is reduced by three-stage vacuum pumping. The overall devolatilization efficiency is not high, and when mixed with other materials and fed from the same feeding port of the extruder, it may cause the expelling agent to be volatilized by premature heating, thereby further weakening the effect of removing VOCs.

[0004] Patent document CN108466383B discloses a polypropylene pellet VOC removal system, which heats the polypropylene pellets by contacting with hot nitrogen in a ridge-type drying tower, so that the volatile substances in the pellets diffuse into the hot nitrogen and are carried away with the hot air flow to achieve the purpose of removing VOCs. However, this method requires a large amount of nitrogen to heat the polypropylene pellets. Due to the poor heating effect and the short residence time in the constant temperature section of the ridge-type drying tower, it is not conducive to the removal of volatile substances in the polypropylene pellets. Summary of the Invention

[0005] The inventor of the present invention unexpectedly found that by using a mixture of nitrogen and water vapor in the devolatilization tower and controlling the composition of the mixture, the heating effect of the pellets can be significantly improved without affecting the physical properties of the synthetic resin particles, the equipment volume can be reduced, the devolatilization effect can be improved, and energy consumption can be saved. Based on this discovery, the purpose of the present invention is to provide a method and a system for deeply removing volatile substances from synthetic resins, with low energy consumption and good devolatilization effect.

[0006] The first aspect of the present invention provides a method for deeply removing volatile substances from synthetic resins, the method comprising:

[0007] The resin particles enter from the top of the ridge-type devolatilization tower, and successively pass through the first heating section, the second heating section and the cooling section of the ridge-type devolatilization tower from top to bottom, and fall to the bottom of the ridge-type devolatilization tower and are discharged;

[0008] After the first mixed gas composed of nitrogen and water vapor passes through the cooling section and directly contacts and exchanges heat with the resin particles, it is pressurized, heated, and steam is supplemented once to obtain the second mixed gas; after the second mixed gas passes through the second heating section and directly contacts and exchanges heat with the resin particles, it is pressurized, heated, and steam is supplemented twice to obtain the third mixed gas; after the third mixed gas passes through the first heating section and directly contacts and exchanges heat with the resin particles, it is cooled, and the obtained gas is discharged and / or recycled to the cooling section, and the condensate enters the sewage treatment system for treatment;

[0009] The partial pressure ratio of nitrogen to water vapor in the first mixed gas is 1:0.1 - 0.35; the partial pressure ratio of nitrogen to water vapor in the second mixed gas is 1:0.45 - 1.45; the partial pressure ratio of nitrogen to water vapor in the third mixed gas is 1:0.45 - 1.45.

[0010] The second aspect of the present invention provides a system for deeply removing volatile substances from synthetic resin adopted by the above method. The system includes a ridge-type devolatilization tower. The top of the ridge-type devolatilization tower is provided with a material inlet, and the bottom is provided with a discharge port. The ridge-type devolatilization tower is successively provided with a first heating section, a second heating section and a cooling section from top to bottom. The first heating section is provided with a first air inlet and a first air outlet, the second heating section is provided with a second air inlet and a second air outlet, and the cooling section is provided with a cooling air inlet and a cooling air outlet;

[0011] The cooling air inlet is connected with a first mixed gas introduction pipeline, and a blower is provided on the first mixed gas introduction pipeline. The cooling air outlet is connected with the second air inlet through a second mixed gas introduction pipeline. A circulation fan I, a second heater and a primary steam supplement pipeline are successively provided on the second mixed gas introduction pipeline; the second air outlet is connected with the first air inlet through a third mixed gas introduction pipeline. A circulation fan II, a first heater and a secondary steam supplement pipeline are successively provided on the third mixed gas introduction pipeline; the first air outlet is connected with a tail gas discharge pipeline and / or a recycling pipeline through a draft fan.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] 1. Compared with using pure hot nitrogen, the mixed gas of nitrogen and water vapor can greatly improve the heat-carrying and heat-transfer effects of the gas. Under the condition that the material processing amount per unit time, the height of the heating section tower and the amount of circulating nitrogen remain unchanged, the temperature change of the resin material can be increased, making it closer to the heating temperature of each heating section.

[0014] 2. Compared with using pure hot nitrogen, the capabilities of equipment such as circulation fans, heaters, and devolatilization towers can be improved.

[0015] 3. Compared with using pure water vapor, a mixed gas of hot nitrogen and water vapor in a certain proportion is used to avoid the condensation of condensed water on the surface of resin pellets and the subsequent drying process of the resin pellets.

[0016] Other features and advantages of the present invention will be described in detail in the following specific implementation section. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic structural diagram of a system for deeply removing volatile substances from synthetic resin according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] The following will describe the specific implementation of the present invention in detail. It should be understood that the specific implementation described herein is only for explaining and understanding the present invention, and is not used to limit the present invention.

[0019] According to the first aspect of the present invention, the present invention provides a method for deeply removing volatile substances from synthetic resin, the method comprising:

[0020] Resin particles enter from the top of the ridge-type devolatilization tower, and sequentially pass through the first heating section, the second heating section and the cooling section of the ridge-type devolatilization tower from top to bottom, and fall to the bottom of the ridge-type devolatilization tower and are discharged;

[0021] A first mixed gas composed of nitrogen and water vapor passes through the cooling section and directly contacts and exchanges heat with the resin particles, and then after pressurization, heating, and primary supplementary steam (the steam is saturated steam at 120 - 135 °C), a second mixed gas is obtained; the second mixed gas passes through the second heating section and directly contacts and exchanges heat with the resin particles, and then after pressurization, heating, and secondary supplementary steam, a third mixed gas is obtained; the third mixed gas passes through the first heating section and directly contacts and exchanges heat with the resin particles, and then after cooling, the obtained gas is discharged and / or returned to the cooling section for recycling, and the condensate (containing volatile organic compounds) enters the sewage treatment system for treatment;

[0022] The partial pressure ratio of nitrogen to water vapor in the first mixed gas is 1:0.1 - 0.35; the partial pressure ratio of nitrogen to water vapor in the second mixed gas is 1:0.45 - 1.45; the partial pressure ratio of nitrogen to water vapor in the third mixed gas is 1:0.45 - 1.45.

[0023] Preferably, the temperature of the second mixed gas is 120 - 135 °C, and the partial pressure ratio of nitrogen to water vapor in the second mixed gas is 1:0.5 - 1.2.

[0024] Preferably, the temperature of the third mixed gas is 120 - 140 °C, and the partial pressure ratio of nitrogen to water vapor in the third mixed gas is 1:0.5 - 1.2.

[0025] In the present invention, the steam supplemented for the first time and the steam supplemented for the second time can be saturated steam at 120-135°C.

[0026] According to the present invention, the temperature of the secondary heating section can be 122-125°C, and the temperature of the primary heating section can be 108-115°C.

[0027] In the present invention, resin particles are transported to a cyclone dust collector through an air conveying system. After being separated by the cyclone dust collector, they enter the feed distributor of the ridge type devolatilization tower. The evenly distributed resin particles flow downward along the primary heating section, the secondary heating section and the cooling section, and finally are discharged through the rotary discharge valve of the ridge type devolatilization tower. The resin particles are on the surface of the ridge type drying pipe in the primary heating section, the secondary heating section and the cooling section, and slowly flow downward through the gaps of the ridge type drying pipe under the action of gravity; the resin particle material with a temperature ≤ 70°C is discharged from the rotary discharge valve, and the discharge speed of the rotary discharge valve is controlled by the weighing control system on the ridge type devolatilization tower to keep the material quantity in the tower constant.

[0028] Since the total amount of the material in the devolatilization tower is certain, the residence time of the material in the devolatilization tower can be adjusted by adjusting the feed amount of the devolatilization. Preferably, the residence time of the resin particles in the primary heating section, the secondary heating section and the cooling section is 40-90 minutes respectively.

[0029] The resin particles are first heated by direct contact with the hot mixed gas in the devolatilization tower, so that the volatile components in the particles diffuse into the hot mixed gas and are carried away by the hot air flow, achieving the purpose of removing the volatile components in the resin pellets; then they are directly contacted and cooled with nitrogen in the cooling section to avoid accelerating the aging of the resin pellets due to too long heating time. The resin pellets are easy to be packaged and stored after being cooled and dried.

[0030] In the present invention, the operation mode of the ridge type devolatilization tower can be intermittent or continuous. When the feeding mode of the ridge type devolatilization tower is continuous feeding, the level height in the ridge type devolatilization tower can be detected and controlled in real time by a weighing module, or a level gauge, or other level detection devices.

[0031] According to the present invention, when the ridge type devolatilization tower has multiple heating sections and multiple cooling sections or no cooling section, the method of the present invention can also be referred to for implementation, and all belong to the protection scope of the present invention.

[0032] The parameters not defined in the present invention can be selected according to the prior art, which belong to the conventional technical means in the field.

[0033] According to the second aspect of the present invention, the present invention provides a system for deeply removing volatile substances from synthetic resin adopted by the above method. The system includes a roof-type devolatilization tower. A material inlet is provided at the top of the roof-type devolatilization tower, and a discharge port is provided at the bottom. The roof-type devolatilization tower is successively provided with a first heating section, a second heating section, and a cooling section from top to bottom. The first heating section is provided with a first air inlet and a first air outlet. The second heating section is provided with a second air inlet and a second air outlet. The cooling section is provided with a cooling air inlet and a cooling air outlet;

[0034] A first mixed gas introduction pipeline is connected to the cooling air inlet. A blower is provided on the first mixed gas introduction pipeline. The cooling air outlet is connected to the second air inlet through a second mixed gas introduction pipeline. A circulation fan I, a second heater, and a primary steam supplement pipeline are successively provided on the second mixed gas introduction pipeline; The second air outlet is connected to the first air inlet through a third mixed gas introduction pipeline. A circulation fan II, a first heater, and a secondary steam supplement pipeline are successively provided on the third mixed gas introduction pipeline; The first air outlet is connected to an exhaust gas discharge pipeline and / or a recycling pipeline through a draft fan.

[0035] Preferably, the system further includes a cyclone dust collector. The pneumatic conveying system of resin particles is connected to the feed inlet of the cyclone dust collector, and the discharge outlet of the cyclone dust collector is connected to the material inlet of the roof-type devolatilization tower.

[0036] In the present invention, a feed distributor is provided at the material inlet, a rotary discharge valve with a speed change device is provided at the discharge port, and a weighing control system is provided on the roof-type devolatilization tower. The weighing control system is electrically connected to the feed distributor and the speed change device respectively.

[0037] According to the present invention, roof-type drying pipes are evenly distributed in the first heating section, the second heating section, and the cooling section of the roof-type devolatilization tower.

[0038] Preferably, both the first heater and the second heater are finned tube heat exchangers and are heated by steam.

[0039] Components not defined in the present invention can be selected according to the prior art and belong to the conventional technical means in the art.

[0040] The following examples are used to further illustrate the present invention, but are not limited by these examples.

[0041] In the following examples and comparative examples, the relevant data are obtained according to the following test methods:

[0042] 1. Melt flow rate (MFR): Measured according to GB / T 3682-2000 using a CEAST 7026 melt index instrument at 230°C under a load of 2.16 kg.

[0043] 2. VOC: According to the method of German Volkswagen test standard VDA277.

[0044] 3. Yellow index: The color coordinate color difference measurement method is used to measure the yellow index by ASTM D2244 together.

[0045] 4. The temperature of each heating section of the devolatilization tower: Measured by a remote thermometer, unit: °C.

[0046] Examples 1-3 are used to illustrate the method and system for deeply removing volatile substances from synthetic resin of the present invention.

[0047] Example 1

[0048] As Figure 1 shown, a system for deeply removing volatile substances from synthetic resin, the system includes a roof-type devolatilization tower 5, the top of the roof-type devolatilization tower 5 is provided with a material inlet, the bottom is provided with a discharge port, and the roof-type devolatilization tower 5 is successively provided with a first heating section 6, a second heating section 7 and a cooling section 8 from top to bottom. The first heating section 6 is provided with a first air inlet and a first air outlet, the second heating section 7 is provided with a second air inlet and a second air outlet, and the cooling section 8 is provided with a cooling air inlet and a cooling air outlet;

[0049] A first mixed gas introduction pipeline 11 is connected to the cooling air inlet, a blower 1 is provided on the first mixed gas introduction pipeline 11, the cooling air outlet is connected to the second air inlet through a second mixed gas introduction pipeline 12, and a circulation fan I 2, a second heater 13 and a primary steam supplement pipeline 14 are successively provided on the second mixed gas introduction pipeline 12; the second air outlet is connected to the first air inlet through a third mixed gas introduction pipeline 15, and a circulation fan II 3, a first heater 16 and a secondary steam supplement pipeline 17 are successively provided on the third mixed gas introduction pipeline 15; the first air outlet is connected to a tail gas discharge pipeline 18 through an induced draft fan 4.

[0050] The system further includes a cyclone dust collector 9. The pneumatic conveying system of resin particles is connected to the feed inlet of the cyclone dust collector 9, and the discharge outlet of the cyclone dust collector 9 is connected to the material inlet of the roof-type devolatilization tower 5.

[0051] A feed distributor (not shown) is provided at the material inlet, a rotary discharge valve 10 with a speed change device is provided at the discharge port, and a weighing control system (not shown) is provided on the roof-type devolatilization tower 5. The weighing control system is electrically connected to the feed distributor and the speed change device respectively.

[0052] Roof-type drying pipes are evenly distributed in the first heating section 6, the second heating section 7 and the cooling section 8 of the roof-type devolatilization tower 5.

[0053] The primary heater 16 and the secondary heater 13 are both finned-tube heat exchangers and are heated by steam.

[0054] A method for deeply removing volatile substances from synthetic resin using the above system, the method comprising:

[0055] Resin particles are transported to the cyclone dust collector 9 through the pneumatic conveying system. After being separated by the cyclone dust collector 9, the resin particles enter the feed distributor from the top of the ridge-type devolatilization tower 5. The evenly distributed resin particles sequentially pass through the primary heating section 6, the secondary heating section 7, and the cooling section 8 of the ridge-type devolatilization tower 5 from top to bottom. The resin particles are on the surface of the ridge-type drying tube and slowly flow downward through the gaps of the ridge-type drying tube under the action of gravity, and finally fall to the bottom of the ridge-type devolatilization tower 5 and are discharged through the rotary discharge valve 10 of the ridge-type devolatilization tower 5.

[0056] The first mixed gas composed of nitrogen and water vapor passes through the cooling section 8 after being pressurized by the blower 1 and directly contacts and exchanges heat with the resin particles, and then passes through the circulation fan I 2 for pressurization, the secondary heater 13 for heating (heated to 128 - 130 °C), and the primary supplementary steam (supplementing saturated steam at 132 - 135 °C) to obtain the second mixed gas; the second mixed gas passes through the secondary heating section 7 and directly contacts and exchanges heat with the resin particles, and then passes through the circulation fan II 3 for pressurization, the primary heater 16 for heating (heated to 132 - 135 °C), and the secondary supplementary steam (supplementing saturated steam at 132 - 135 °C) to obtain the third mixed gas; the third mixed gas passes through the primary heating section 6 and directly contacts and exchanges heat with the resin particles, and then is led out by the induced draft fan 4, cooled, and the obtained gas is discharged, and the condensate enters the sewage treatment system for treatment;

[0057] The partial pressure ratio of nitrogen to water vapor in the first mixed gas is 1:0.3; the partial pressure ratio of nitrogen to water vapor in the second mixed gas is 1:0.7; the partial pressure ratio of nitrogen to water vapor in the third mixed gas is 1:1.

[0058] The temperature of the secondary heating section is 125 °C, and the temperature of the primary heating section is 115 °C.

[0059] The residence time of the resin particles in the primary heating section 6, the secondary heating section 7, and the cooling section 8 is 60 minutes respectively.

[0060] The performance of the resin particles after devolatilization using the above method and system is shown in Table 1.

[0061] Examples 2 - 3

[0062] Same as Example 1, the difference is that: the partial pressure ratios of nitrogen to water vapor in the first mixed gas, the second mixed gas, and the third mixed gas are different; the temperatures of the secondary heating section and the primary heating section are different, and the specific parameters and the performance of the resin particles after devolatilization are shown in Table 1.

[0063] Comparative Examples 1 - 3

[0064] Same as Example 1, except that: the partial pressure ratios of nitrogen to water vapor in the first mixed gas, the second mixed gas, and the third mixed gas are different; the temperatures of the secondary heating section and the primary heating section are different. The specific parameters and the properties of the resin particles after devolatilization are shown in Table 1.

[0065] Table 1

[0066]

[0067] As can be seen from Table 1, by using the method of the present invention to perform VOC removal on the synthetic resin, the VOC content of the resin pellets can be reduced, and the color of the resin pellets basically remains unchanged. By selecting the partial pressure ratio of nitrogen to water vapor of the present invention in each mixed gas, a better VOC removal effect can be obtained.

[0068] The embodiments of the present invention have been described above. The above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations are obvious to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for deeply removing volatile substances from synthetic resin, characterized in that, The method includes: Resin particles enter from the top of the ridge-type devolatilization tower and sequentially pass through the first-stage heating section, the second-stage heating section, and the cooling section of the ridge-type devolatilization tower from top to bottom, and fall to the bottom of the ridge-type devolatilization tower for discharge; the temperature of the second-stage heating section is 123 - 125 °C, and the temperature of the first-stage heating section is 112 - 115 °C; the residence times of the resin particles in the first-stage heating section, the second-stage heating section, and the cooling section are 40 - 90 min respectively; After the first mixed gas composed of nitrogen and water vapor passes through the cooling section and directly contacts and exchanges heat with the resin particles, it is pressurized, heated, and supplemented with steam once to obtain the second mixed gas; after the second mixed gas passes through the second-stage heating section and directly contacts and exchanges heat with the resin particles, it is pressurized, heated, and supplemented with steam twice to obtain the third mixed gas; after the third mixed gas passes through the first-stage heating section and directly contacts and exchanges heat with the resin particles, it is cooled, and the obtained gas is discharged and / or recycled back to the cooling section, and the condensate enters the sewage treatment system for treatment; The partial pressure ratio of nitrogen to water vapor in the first mixed gas is 1:0.3; the partial pressure ratio of nitrogen to water vapor in the second mixed gas is 1:0.7 - 0.8; the partial pressure ratio of nitrogen to water vapor in the third mixed gas is 1:0.9 - 1.

0.

2. The method for deeply removing volatile substances from synthetic resin according to claim 1, wherein, The resin particles are transported to the cyclone dust collector through the pneumatic conveying system. After being separated by the cyclone dust collector, they enter the feed distributor of the ridge-type devolatilization tower. The evenly distributed resin particles flow downward along the first-stage heating section, the second-stage heating section, and the cooling section, and finally are discharged through the rotary discharge valve of the ridge-type devolatilization tower.

3. The method for deeply removing volatile substances from synthetic resin according to claim 1, wherein, The system for deeply removing volatile substances from synthetic resin used in the described method includes a ridge-type devolatilization tower. The top of the ridge-type devolatilization tower is provided with a material inlet, and the bottom is provided with a discharge port. The ridge-type devolatilization tower is sequentially provided with a first-stage heating section, a second-stage heating section, and a cooling section from top to bottom. The first-stage heating section is provided with a first-stage air inlet and a first-stage air outlet, the second-stage heating section is provided with a second-stage air inlet and a second-stage air outlet, and the cooling section is provided with a cooling air inlet and a cooling air outlet; The cooling air inlet is connected to a first mixed gas introduction pipeline, and a blower is provided on the first mixed gas introduction pipeline. The cooling air outlet is connected to the second-stage air inlet through a second mixed gas introduction pipeline. A circulation fan I, a second-stage heater, and a primary steam supplement pipeline are sequentially provided on the second mixed gas introduction pipeline; the second-stage air outlet is connected to the first-stage air inlet through a third mixed gas introduction pipeline. A circulation fan II, a first-stage heater, and a secondary steam supplement pipeline are sequentially provided on the third mixed gas introduction pipeline; the first-stage air outlet is connected to a tail gas discharge pipeline and / or a recycling pipeline through a draft fan.

4. The method for deeply removing volatile substances from synthetic resin according to claim 3, wherein, The system includes a cyclone dust collector. The pneumatic conveying system of the resin particles is connected to the feed inlet of the cyclone dust collector, and the discharge outlet of the cyclone dust collector is connected to the material inlet of the ridge-type devolatilization tower.

5. The method for deeply removing volatile substances from synthetic resin according to claim 4, wherein, A feed distributor is provided at the material inlet, a rotary discharge valve with a speed-changing device is provided at the discharge port, and a weighing control system is provided on the ridge-type devolatilization tower. The weighing control system is electrically connected to the feed distributor and the speed-changing device respectively.

6. The method for deep removal of volatile substances from synthetic resin according to claim 3, wherein, The first-stage heating section, the second-stage heating section and the cooling section of the ridge-type devolatilization tower are all evenly provided with ridge-type drying tubes; both the first-stage heater and the second-stage heater are finned tube heat exchangers.

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