Exhaust emission system in polyolefin device
By combining a closed-loop nitrogen delivery system for powder with an injector, the problem of hydrocarbon gas emissions in polyolefin plants has been solved. This has effectively reduced the content of volatile organic compounds and odor without increasing consumption, thereby improving production safety and product competitiveness.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-11
- Publication Date
- 2026-04-07
AI Technical Summary
In existing technologies, the problem of volatile organic compound emissions in polyolefin plants is difficult to solve effectively. In particular, the pressure of hydrocarbon gases released from the extrusion granulation unit is insufficient, making it impossible to directly enter the waste gas treatment system. Furthermore, the use of inert gas purging is ineffective, or the vacuum suction system is prone to explosion risks.
A closed-loop nitrogen conveying system for powder is combined with an injector. Nitrogen is used as the working fluid to mix and pressurize hydrocarbon gases, and the hydrocarbon gases are directly discharged into the waste gas treatment system, avoiding additional gas source consumption and mechanical energy consumption. The injector generates negative pressure to draw in and accelerate the delivery into the treatment system.
It effectively reduces volatile organic compound content and odor without increasing gas supply and mechanical energy consumption, improves production safety, reduces the impact on the surrounding environment, simplifies the equipment structure, and reduces costs.
Smart Images
Figure CN121797709A_ABST
Abstract
Description
Technical Field
[0001] This application belongs to the field of petrochemical waste gas treatment technology, specifically relating to a waste gas emission system in a polyolefin plant. Background Technology
[0002] In the polyolefin plants of petrochemical enterprises, the generation and emission of volatile organic compounds (VOCs) has always been a key concern in the industry and one of the current challenges in environmental governance. The production process of polyolefins, such as the polymerization reactions of polyethylene and polypropylene, and subsequent extrusion granulation, generates large amounts of waste gas containing VOCs. These waste gases are not only high in organic matter and complex in composition, encompassing various hydrocarbons and oxygen-containing organic compounds such as ethylene, propylene, butene, hexene, methylcyclopentane, and methanol, but also have low odor thresholds and strong, often irritating or foul-smelling odors, easily causing significant impacts on the plant area and surrounding environment.
[0003] To improve the safety of the production process and the competitiveness of products in the market, the insufficient removal capacity of residual hydrocarbon gases in the powder of the upstream process can be made up by performing devolatilization on the process materials in the extrusion granulation section.
[0004] To reduce the volatile organic compound (VOC) content and odor in the extrusion granulation section, existing technologies typically employ two methods: one is to use a vacuum suction system powered by a liquid ring vacuum pump to extract the unit's exhaust gases; the other is to use inert gas to purge the exhaust gases at the emission source, directing them downstream. The first method, using a vacuum suction system, is prone to causing the accumulation of Class A materials, impacting the classification of surrounding explosion hazard zones and the categorization of buildings and structures. The second method, using inert gas purging, suffers from limitations in the unit's exhaust section's mechanical structure to guarantee effective purging; the purging pressure cannot be too high, resulting in insufficient pressure for the extracted hydrocarbon gases, preventing them from directly entering the waste gas treatment system and thus causing inadequate hydrocarbon removal capacity.
[0005] In view of this, we propose an exhaust gas emission system for polyolefin plants to solve the above problems. Summary of the Invention
[0006] This application provides an exhaust gas emission system for a polyolefin plant. It aims to achieve the emission of desorbed hydrocarbon gases without increasing gas source consumption or mechanical energy consumption.
[0007] This application provides an exhaust gas emission system for a polyolefin plant, comprising: A closed-loop nitrogen conveying system for powder materials is equipped with an exhaust end; Extrusion granulation unit, used to remove hydrocarbon gases; The exhaust gas branch has an exhaust gas branch inlet and an exhaust gas branch outlet, wherein the exhaust gas branch inlet is connected to the hydrocarbon gas removed from the extrusion granulation unit; The power branch includes a first branch, which has a first branch inlet and a first branch outlet. The first branch inlet is used to connect with the exhaust end of the powder nitrogen conveying system. The exhaust gas treatment system is equipped with an exhaust gas treatment inlet; The injector is provided with a first inlet connected to the exhaust gas branch outlet, a second inlet connected to the first branch outlet, and a mixing outlet connected to the exhaust gas treatment inlet. In this system, the gas source at the exhaust end of the powder nitrogen conveying system is mixed with the hydrocarbon gas from the waste gas branch in the injector, so as to draw and pressurize the hydrocarbon gas from the mixing outlet of the injector and discharge it to the waste gas treatment system.
[0008] In some embodiments, the power branch includes a first flow-limiting orifice plate disposed on the first branch, the first flow-limiting orifice plate being located upstream of the second inlet of the injector.
[0009] In some embodiments, the power branch further includes an exhaust branch connected in parallel with the first branch. The exhaust branch is equipped with a first flow regulating valve. The inlet of the exhaust branch is connected to the exhaust end of the powder nitrogen conveying system, and the outlet of the exhaust branch is connected to the exhaust gas treatment inlet of the waste gas treatment system.
[0010] In some embodiments, the first branch is further provided with a pressure transmitter located upstream of the first flow-limiting orifice plate.
[0011] In some embodiments, the exhaust gas system in the polyolefin plant further includes a controller that is signal-connected to the pressure transmitter and the first flow regulating valve.
[0012] In some embodiments, the power branch further includes a nitrogen source and a second branch connected to the nitrogen source; The second branch is connected in parallel with the first branch, and the second branch is connected to the second inlet of the injector.
[0013] In some embodiments, the power branch further includes a second flow limiting orifice plate and a switching valve disposed on the second branch, wherein the second flow limiting orifice plate is located downstream of the switching valve and upstream of the injector.
[0014] In some embodiments, the exhaust gas treatment system further includes a connecting pipe and a one-way valve disposed on the connecting pipe, the connecting pipe being located between the mixing outlet of the injector and the exhaust gas treatment system.
[0015] In some embodiments, the exhaust gas branch further includes a condenser body, which has a cooling water inlet, a cooling water outlet, a gas phase inlet, and a gas phase outlet. The gas phase inlet of the condenser body is used to communicate with the hydrocarbon gas removed from the extrusion granulator unit, and the gas phase outlet of the condenser body is connected to the first inlet of the ejector.
[0016] In some embodiments, the exhaust gas treatment system includes at least one of a low-pressure flare, an RTO system, a VCU system, and a CEB system.
[0017] In some embodiments, the injector further includes: A receiving chamber, wherein the receiving chamber is equipped with a nozzle; The mixing chamber is in communication with the nozzle; and, The diffuser is connected to both the mixing chamber and the exhaust gas treatment system. The first inlet and the second inlet are located in the receiving chamber, and the mixing outlet is located in the diffuser.
[0018] In some embodiments, the powder nitrogen delivery system includes a powder nitrogen delivery pipeline connected to the nitrogen pipeline, a compressor and a heat exchanger disposed in the powder nitrogen delivery pipeline, wherein the inlet of the compressor is connected to the nitrogen pipeline, the outlet of the compressor is connected to the inlet of the heat exchanger, and the outlet of the heat exchanger is connected to a first branch of the exhaust gas emission system.
[0019] In some embodiments, the powder nitrogen conveying pipeline is further provided with a second flow regulating valve, which is located upstream of the first branch.
[0020] According to one or more embodiments of this application, a waste gas emission system for a polyolefin plant is provided, including a closed-loop nitrogen conveying system for powder, an extrusion granulator, a waste gas branch, a power branch, a waste gas treatment system, and an ejector. The closed-loop nitrogen conveying system for powder has an exhaust end. The extrusion granulator is used to remove hydrocarbon gases. The waste gas branch has a waste gas branch inlet and a waste gas branch outlet. The waste gas branch inlet is used to communicate with the hydrocarbon gases removed by the extrusion granulator. The power branch includes a first branch, which has a first branch inlet and a first branch outlet. The first branch inlet is used to communicate with the exhaust end of the nitrogen conveying system for powder. The waste gas treatment system has a waste gas treatment inlet. The ejector has a first inlet communicating with the outlet of the waste gas branch, a second inlet communicating with the outlet of the first branch, and a mixing outlet communicating with the waste gas treatment inlet. The gas source at the exhaust end of the nitrogen conveying system for powder is mixed with the hydrocarbon gases from the waste gas branch in the ejector to draw and pressurize the hydrocarbon gases from the mixing outlet of the ejector and discharge them to the waste gas treatment system.
[0021] This application connects the first branch inlet to the exhaust end of the powder nitrogen conveying system, allowing nitrogen from the closed-loop powder nitrogen conveying system to be transported via the first branch to the second inlet of the ejector. Simultaneously, the hydrocarbon gas from the extrusion granulator is connected to the exhaust gas branch, allowing the hydrocarbon gas from the extrusion granulator to be sent via the exhaust gas branch to the second inlet of the ejector. Nitrogen from the closed-loop powder nitrogen conveying system serves as the working fluid, and the hydrocarbon gas from the extrusion granulator serves as the ejector fluid. The two are mixed and pressurized in the ejector to form a mixed compressed fluid, which is then discharged to the downstream exhaust gas treatment system. This achieves the purpose of removing hydrocarbon gases volatilized from the extrusion granulator section, thereby reducing the volatile organic compound content and product odor. Attached Figure Description
[0022] Figure 1 A schematic diagram of the exhaust gas emission system in a polyolefin plant according to one or more embodiments of this application is shown.
[0023] Figure 2 It shows Figure 1 A partial schematic diagram of the exhaust gas emission system in a polyolefin plant.
[0024] Figure 3 It shows Figure 1 A schematic diagram of one embodiment of the exhaust gas emission system in a polyolefin plant.
[0025] Figure 4 It shows Figure 1 A schematic diagram of another embodiment of the exhaust gas emission system in a polyolefin plant.
[0026] Explanation of reference numerals in the attached drawings: 100 - Exhaust gas emission system in the polyolefin unit; 110 - Exhaust gas branch; 111 - Condenser body; 120 - Power branch; 121 - First branch; 122 - First flow restrictor plate; 123 - Emission branch; 124 - First flow regulating valve; 125 - Pressure transmitter; 126 - Second branch; 127 - Second flow restrictor plate; 128 - Switch valve; 129 - Nitrogen source; 130 - Exhaust gas treatment system; 131 - Check valve; 140 - Injector; 200 - Closed-loop nitrogen conveying system for powder; 210 - Compressor; 220 - Heat exchanger; 230 - Second flow regulating valve; 300 - Extrusion granulation unit. Detailed Implementation
[0027] To enable those skilled in the art to more clearly understand this application, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.
[0028] In polyolefin plants of petrochemical enterprises, volatile gases are generated. Currently, the market typically uses vacuum suction systems powered by liquid ring vacuum pumps to extract the unit's exhaust gases. However, using vacuum suction systems can easily lead to the accumulation of Class A materials, affecting the classification of surrounding explosion hazard zones and the classification of buildings and structures. Alternatively, inert gas can be used to purge the unit's exhaust gases at the emission source, directing them downstream. However, the purging pressure should not be too high, resulting in excessively low pressure for the extracted hydrocarbon gases, preventing them from directly entering the waste gas treatment system and compromising purging effectiveness.
[0029] In view of this, we propose an exhaust gas emission system for polyolefin plants to solve the above problems.
[0030] This invention proposes a waste gas emission system for polyolefin plants, which aims to achieve the emission of desorbed hydrocarbon gases without increasing gas source consumption and mechanical energy consumption.
[0031] Please see Figure 1 , Figure 2 , Figure 3 and Figure 4According to a first aspect of this application, an exhaust gas emission system 100 for a polyolefin plant is provided. The exhaust gas emission system 100 includes a closed-loop nitrogen conveying system 200 for powder, an extrusion granulator unit 300, an exhaust gas branch 110, a power branch 120, an exhaust gas treatment system 130, and an injector 140. The closed-loop nitrogen conveying system 200 for powder is provided with an exhaust end; the extrusion granulator unit 300 is used to remove hydrocarbon gases; the exhaust gas branch 110 is provided with an exhaust gas branch 110 inlet and an exhaust gas branch 110 outlet, the exhaust gas branch 110 inlet being connected to the hydrocarbon gases removed by the extrusion granulator unit 300; the power branch 120 includes a first... Branch 121, the first branch 121 has a first branch 121 inlet and a first branch 121 outlet. The first branch 121 inlet is used to connect with the exhaust end of the powder nitrogen conveying system; the waste gas treatment system 130 has a waste gas treatment inlet; the ejector 140 has a first inlet connected to the outlet of the waste gas branch 110, a second inlet connected to the outlet of the first branch 121, and a mixing outlet connected to the waste gas treatment inlet; wherein, the gas source at the exhaust end of the powder nitrogen conveying system and the hydrocarbon gas of the waste gas branch 110 are mixed in the ejector 140, so that the hydrocarbon gas is drawn and pressurized from the mixing outlet of the ejector 140 and discharged to the waste gas treatment system 130.
[0032] Polyolefin plants typically include the following process units: reaction unit, refining system, catalyst system, degassing system, recovery unit, powder conveying system, additive system, extrusion granulation system, pellet conveying system, and packaging unit. This application applies the closed-loop nitrogen conveying system for powder in the powder conveying system and the extrusion granulation system to the exhaust gas emission system of the polyolefin plant, thereby enabling the treatment and emission of hydrocarbon gases released from the extrusion granulation unit.
[0033] The hydrocarbon gases removed from the extrusion granulator unit 300 are mainly non-methane total hydrocarbons, containing low-molecular-weight olefins and alkanes. In the prior art, the hydrocarbon gases removed from the extrusion granulator unit 300 are usually extracted by a vacuum suction system powered by a liquid ring vacuum pump. This application, without using a liquid ring vacuum pump or other mechanical energy consumption, provides nitrogen through the closed-loop nitrogen conveying system 200 of the extrusion granulator unit 300. The nitrogen is introduced into the ejector 140 as a working fluid. The hydrocarbon gases removed from the extrusion granulator unit 300 are used as the ejector fluid. The hydrocarbon gases and the nitrogen in the closed-loop nitrogen conveying system 200 are mixed and pressurized in the ejector 140 to form a mixed compressed fluid, which is then discharged to the downstream waste gas treatment system 130. This achieves the purpose of removing the hydrocarbon gases volatilized from the extrusion granulator section, thereby reducing the volatile organic compound content and reducing the product odor.
[0034] In the closed-loop nitrogen delivery system 200 for powder materials, most of the nitrogen is recycled. When the amount of combustible hydrocarbons, such as propylene, in the recycled gas accumulates to approximately 1% LEL (Less than the lowest concentration at which a combustible gas can explode in air), the nitrogen is released. Below this concentration, the gas mixture is too lean to ignite; at or above the LEL, there is a risk of explosion upon contact with an ignition source. In existing technology, when the amount of combustible hydrocarbons, such as propylene, in the recycled gas accumulates to approximately 1% LEL, the nitrogen vent valve in the closed-loop nitrogen delivery system 200 can be automatically opened to send a portion of the hydrocarbon-containing nitrogen to an RTO, flare, or boiler fuel gas system for combustion. After reaching the required standard, the nitrogen is discharged through an exhaust stack. Simultaneously, an equal amount of fresh nitrogen is added to the closed-loop nitrogen delivery system 200 to maintain the pressure balance.
[0035] The closed-loop nitrogen conveying system 200 for powder materials usually maintains a constant exhaust volume to avoid the accumulation of hydrocarbon gases and the increase of oxygen concentration in the closed-loop system. In this application, pressurized nitrogen in the closed-loop nitrogen conveying system 200 for powder materials is used as the working fluid of the ejector 140. That is, the working fluid of the ejector 140 offsets part of this constant exhaust volume, thereby achieving the extraction, pressurization and discharge of hydrocarbon gases released from the extrusion granulator unit 300 without increasing the gas source consumption of the device.
[0036] This application utilizes the nitrogen that needs to be discharged from the closed-loop nitrogen conveying system 200 for powder production. The nitrogen is conveyed to the injector 140 via the first branch 121 as a working fluid, thus reusing the discharged nitrogen to power the hydrocarbon gases extruded from the extrusion granulator 300. Compared to existing technologies that use inert gases to purge the exhaust gases at the emission source and direct them downstream, this application eliminates the need for additional inert gases, saving costs.
[0037] The injector 140 uses a high-speed nitrogen jet to generate negative pressure, which draws in the hydrocarbon gas released from the extrusion granulator 300 and accelerates its delivery into the waste gas treatment system 130, thereby removing the hydrocarbon gas volatilized from the extrusion granulator section, thus reducing the volatile organic compound content and minimizing the product odor.
[0038] The exhaust gas treatment system 130 can collect the mixed gas from the outlet of the ejector 140 and purify the exhaust gas through physical or chemical methods before discharging it after it meets the standards.
[0039] Therefore, this application connects the inlet of the first branch 121 to the exhaust end of the powder nitrogen conveying system, so that the nitrogen in the closed-loop powder nitrogen conveying system 200 is conveyed to the second inlet of the ejector via the first branch 121. At the same time, the hydrocarbon gas released from the extrusion granulator 300 is connected to the exhaust gas branch 110, so that the hydrocarbon gas released from the extrusion granulator 300 is sent to the second inlet of the ejector 140 via the exhaust gas branch 110. The nitrogen in the closed-loop powder nitrogen conveying system 200 is used as the working fluid, and the hydrocarbon gas released from the extrusion granulator 300 is used as the ejector fluid. The two are mixed and pressurized in the ejector to form a mixed compressed fluid, which is then discharged to the downstream exhaust gas treatment system 130. This achieves the purpose of removing the hydrocarbon gas volatilized from the extrusion granulator section, thereby reducing the volatile organic compound content and reducing the product odor.
[0040] In some embodiments, the power branch 120 includes a first flow-limiting orifice plate 122 disposed on the first branch 121, the first flow-limiting orifice plate 122 being located upstream of the second inlet of the injector 140. That is, by setting the first flow-limiting orifice plate 122 before the nitrogen in the first branch 121 enters the second inlet of the injector 140, the pressure and flow rate of the nitrogen in the first branch 121 can be stabilized, ensuring that nitrogen continuously and in a constant quantity enters the injector 140 through the second inlet. This reduces the risk of device shutdown due to ejection ratio imbalance caused by gas source fluctuations, thereby improving the reliability of the entire system.
[0041] In some embodiments, the first flow-limiting orifice plate 122 includes a first plate body and a plurality of first through holes disposed on the first plate body. The first through holes can be evenly distributed in a circumferential array along the first plate body, and the first through holes are opened along the thickness direction of the first plate body. It should be noted that the number of first through holes is not specifically limited in this embodiment, and can be flexibly set according to actual working needs, the overall performance requirements of the powder closed-loop nitrogen conveying system 200 and the exhaust gas emission system; different numbers of through holes will affect the pressure distribution and flow distribution of the working fluid. Therefore, in practical applications, the most suitable number of through holes can be determined through experiments or simulation calculations to ensure that the exhaust gas emission system can operate efficiently and stably.
[0042] In some embodiments, the power branch 120 further includes a discharge branch 123 connected in parallel with the first branch 121. The discharge branch 123 is equipped with a first flow regulating valve 124. The inlet of the discharge branch 123 is connected to the exhaust end of the powder nitrogen conveying system, and the outlet of the discharge branch 123 is connected to the exhaust gas treatment inlet of the exhaust gas treatment system 130. By setting the discharge branch 123 in parallel with the first branch 121 in the power branch 120, if the flow rate of the working fluid drawn from the upstream powder closed-loop nitrogen conveying system 200 is too large, the excess gas can be discharged to the exhaust gas treatment system 130 by opening the first flow regulating valve 124, thus ensuring the stable operation of the entire system.
[0043] In some embodiments, the opening degree of the first flow regulating valve 124 is 0~100%. The opening degree of the first flow regulating valve 124 can be opened according to the actual situation. The opening degree of the first flow regulating valve 124 can be 0, 10%, 13%, 20%, 25%, 28%, 30%, 35%, 42%, 48%, 50%, 59%, 67%, 72%, 85%, 93% or 100%.
[0044] To facilitate timely acquisition of the flow rate of the working fluid in the first branch 121, in some embodiments, the first branch 121 is further equipped with a pressure transmitter 125, which is located upstream of the first flow-limiting orifice plate 122. The pressure transmitter 125 can acquire the flow rate value upstream of the first flow-limiting orifice plate 122. When the flow rate value upstream of the first flow-limiting orifice plate 122 is greater than a preset value, the first flow regulating valve 124 can be opened, i.e., the opening degree of the first flow regulating valve 124 can be controlled so that the flow rate value upstream of the first flow-limiting orifice plate 122 meets the normal operating requirements of the ejector 140. When the flow rate value upstream of the first flow-limiting orifice plate 122 is equal to or less than the preset value, the opening degree of the first flow regulating valve 124 can be set to 0%. Under normal circumstances, the flow rate value upstream of the first flow-limiting orifice plate meets the normal operating requirements of the ejector 140.
[0045] Understandably, the preset value is the critical value of the working fluid flow rate for normal operation of ejector 140. Under normal circumstances, the flow rate upstream of the first flow limiter is within a reasonable range required for normal operation of the ejector.
[0046] In addition, the pressure transmitter 125 can obtain the pressure value upstream of the first flow limiting orifice plate 122 and convert the pressure value upstream of the first flow limiting orifice plate 122 into a volumetric flow rate value. The throttling condition of the first flow limiting orifice plate 122 is limited. If the load of the powder nitrogen conveying system increases, resulting in an increase in flow rate, in order to ensure that the load of the ejector fluid and working fluid in the ejector 140 meets the actual working requirements, when the flow rate value upstream of the first flow limiting orifice plate 122 is greater than the preset value, the first flow regulating valve 124 can be controlled to open. That is, some of the excess nitrogen can be discharged into the waste gas treatment system 130 through a branch for waste gas treatment, instead of directly introducing the excess nitrogen into the ejector 140, which would result in a large load on the ejector 140 and affect the normal operation of the ejector 140.
[0047] In some embodiments, the exhaust gas emission system 100 in the polyolefin plant further includes a controller, which is signal-connected to the pressure transmitter 125 and the first flow regulating valve 124. That is, the controller can obtain the flow rate value from the pressure transmitter 125, thereby controlling the opening degree of the first flow regulating valve 124. Through pressure interlock control, the controller interlocks the pressure transmitter 125 and the first flow regulating valve 124, allowing excess gas to be discharged to the exhaust gas treatment system 130, ensuring the normal operating requirements of the ejector 140.
[0048] Therefore, by setting a discharge branch 123 upstream of the first flow-limiting orifice plate 122 of the first branch 121, the excess load of nitrogen can be released through the branch, avoiding an increase in flow rate due to an increase in the load of the powder nitrogen conveying system, which would affect the normal operation of the ejector 140. That is, while ensuring the normal operation of the ejector, the stability of the entire system is guaranteed.
[0049] In some embodiments, the power branch 120 further includes a nitrogen source 129 and a second branch 126 connected to the nitrogen source 129; the second branch 126 is connected in parallel with the first branch 121 and is connected to the second inlet of the ejector 140. By providing the second branch 126 in parallel with the first branch 121, the nitrogen source 129 of the second branch 126 can meet the normal flow requirements of the ejector. When the upstream closed-loop nitrogen conveying system 200 for powder is under maintenance and cannot provide working fluid to the ejector 140, in order to ensure normal exhaust gas treatment of the degassing section of the extrusion granulator unit 300, the second branch 126 can be opened, and nitrogen source 129 of the second branch 126 can be used to provide nitrogen to the ejector 140 as working fluid. That is, when the upstream closed-loop nitrogen conveying system 200 for powder cannot provide nitrogen, nitrogen can be provided through the second branch 126 to ensure normal exhaust gas treatment of the degassing section of the extrusion granulator unit 300.
[0050] In some embodiments, the nitrogen source 129 can directly use the common engineering nitrogen in the polyolefin unit 10, without the need for additional compressor units or nitrogen cylinder groups, thus simplifying the entire system and apparatus.
[0051] In some embodiments, the power branch 120 further includes a second flow-limiting orifice plate 127 and a switching valve 128 disposed on the second branch 126. The second flow-limiting orifice plate is located downstream of the switching valve 128, and the second flow-limiting orifice plate 127 is located upstream of the injector 140, that is, the outlet of the second flow-limiting orifice plate 127 is connected to the second inlet of the injector 140. That is, when the upstream closed-loop nitrogen conveying system 200 for powder cannot provide nitrogen, nitrogen from the second branch 126 can be input into the injector 140 by opening the switching valve 128, ensuring normal exhaust gas treatment of the degassing section of the extrusion granulator unit 300. The second flow-limiting orifice plate 127 can stabilize the pressure and flow rate of nitrogen in the second branch 126, ensuring that nitrogen continuously and in a constant amount enters the injector 140 through the second inlet, reducing the risk of equipment shutdown caused by injection ratio imbalance due to gas source fluctuations, thereby improving the reliability of the entire system.
[0052] In some embodiments, the second flow-limiting orifice plate 127 includes a second plate body and a plurality of second through holes disposed on the second plate body. The second through holes can be evenly distributed in a circumferential array along the second plate body, and the second through holes are opened along the thickness direction of the second plate body. It should be noted that the number of second through holes is not specifically limited in this embodiment, and can be flexibly set according to actual working needs, the overall performance requirements of the powder closed-loop nitrogen conveying system 200 and the exhaust gas emission system. Different numbers of through holes will affect the pressure distribution and flow distribution of the working fluid. Therefore, in practical applications, the most suitable number of through holes can be determined through experiments or simulation calculations to ensure that the exhaust gas emission system can operate efficiently and stably.
[0053] In some embodiments, the exhaust gas treatment system 130 further includes a connecting pipe and a one-way valve 131 disposed on the connecting pipe. The connecting pipe is located between the mixing outlet of the ejector 140 and the exhaust gas treatment system 130. By providing a connecting pipe between the ejector 140 and the exhaust gas treatment system 130, it is ensured that the mixed high-speed fluid can be output through the connecting pipe, providing a stable path. The one-way valve 131 disposed on the connecting pipe can be used to prevent backflow of combustible gas in the downstream exhaust gas treatment system 130, thereby improving reliability.
[0054] In some embodiments, the exhaust gas branch 110 further includes a condenser body 111, which has a cooling water inlet, a cooling water outlet, a gas phase inlet, and a gas phase outlet. The gas phase inlet of the condenser body is used to communicate with the hydrocarbon gas removed from the extrusion granulator unit 300, and the gas phase outlet of the condenser body 111 is connected to the first inlet of the ejector 140. The hydrocarbon gas removed from the extrusion granulator unit 300 is condensed by the condenser, which can precipitate heavy hydrocarbon components and water at the operating temperature, ensuring that the ejector fluid entering the ejector 140 is gaseous. If heavy hydrocarbon components and water enter the ejector 140, it may cause blockage of the ejector 140. Water in natural gas and hydrocarbons are prone to form ice crystal-like hydrates under high pressure and low temperature conditions, and may also precipitate liquid or solid hydrocarbons due to the condensation of heavy hydrocarbons. These solid particles will deposit in narrow parts such as the neck and annular gap of the ejector 140, causing mechanical blockage, causing a sharp drop in ejector air volume or even complete loss of ejector capability. Furthermore, heavy hydrocarbons, especially olefins and aromatics, are prone to carbonization and desorption in high-temperature, high-speed gas flows, forming viscous deposits such as asphaltenes and coke. If water droplets are also entrained, local temperature fluctuations will exacerbate the coking rate, further reducing the flow cross-section and ultimately causing carbon buildup and blockage of the injector 140. Therefore, this application utilizes a condenser to recover heavy hydrocarbons and water, preventing them from entering the injector 140 and causing blockage, thus ensuring the stability of the entire system.
[0055] In some embodiments, the exhaust gas treatment system 130 includes at least one of a low-pressure flare, an RTO system, a VCU system, and a CEB system. The low-pressure flare primarily maintains a slight positive pressure at the flare head using a water seal / molecular seal. After leaving the nozzle, the exhaust gas is entrained by the surrounding air and undergoes continuous combustion at 800°C to 1000°C in the open flame zone. The RTO (Regenerative Thermal Oxidizer) system refers to a regenerative thermal oxidizer, which mainly utilizes a ceramic regenerator to preheat the exhaust gas to 760–850°C. In the combustion chamber, VOCs are oxidized at high temperature to CO2 and H2O, and most of the heat is recovered through periodic switching of the airflow direction, achieving self-heating operation. The VCU (Volatile Combustion Unit) system directly introduces VOC exhaust gas into the refractory furnace, where it comes into contact with the natural gas burner flame, completing oxidation at 800°C to 1100°C within 0.3–0.5 seconds. CEB (Certified Ultra-Low Emissions Burner) system refers to ultra-low emission metal fiber surface incineration facilities. The principle is fully premixed metal fiber surface combustion. After the exhaust gas and air are fully mixed, surface combustion is carried out on a special burner head. The entire metal fiber burner is a burner head, and the flame area is basically the same as the burner area. The flame completely covers the burner, and the combustion temperature is 900~1300℃.
[0056] Therefore, organic pollutants and odorous substances in waste gas can be effectively removed by incineration through any of the following systems: low-pressure flare, RTO system, VCU system, and CEB system, thereby reducing the degree of pollution of the waste gas to the environment.
[0057] In some implementations, the ejector 140 also includes a receiving chamber, a mixing chamber, and a diffuser. The receiving chamber is equipped with a nozzle; the mixing chamber is connected to the nozzle; and the diffuser is connected to both the mixing chamber and the exhaust gas treatment system 130. The first and second inlets are located in the receiving chamber, and the mixing outlet is located in the diffuser. By providing a receiving chamber in the ejector 140, the working fluid can be received. The working fluid enters the nozzle and accelerates in the constriction section of the nozzle, forming a high-speed, low-pressure jet. The high-speed jet at the nozzle outlet causes a significant pressure drop in the surrounding area, thereby drawing the ejected fluid (i.e., the hydrocarbon gas extruded from the extrusion granulator 300) into the receiving chamber. The working fluid and the ejected fluid mix in the mixing chamber. In the mixing chamber, the working fluid drives the ejected fluid, and through intense shearing, collision, and momentum exchange, they gradually mix and reach an intermediate velocity and pressure state. The diffuser decelerates the high-speed mixed fluid, converting kinetic energy into pressure energy, thereby increasing the pressure of the mixed fluid, which is then discharged to the exhaust gas treatment system 130 for treatment.
[0058] In some embodiments, the powder nitrogen conveying system includes a powder nitrogen conveying pipeline connected to a nitrogen pipeline, a compressor 210 and a heat exchanger 220 disposed on the powder nitrogen conveying pipeline. The inlet of the compressor 210 is connected to the nitrogen pipeline, the outlet of the compressor 210 is connected to the inlet of the heat exchanger 220, and the outlet of the heat exchanger 220 is connected to the first branch 121 of the exhaust gas emission system. The inlet of the compressor 210 is connected to the nitrogen pipeline, meaning that the nitrogen in the nitrogen pipeline can be pressurized by the compressor 210 to ensure that the nitrogen still has a high pressure when it reaches the injector 140, thereby forming a jet and generating negative pressure, which facilitates the extraction and accelerated delivery of hydrocarbon gases from the extrusion granulator unit 300 into the exhaust gas treatment system 130.
[0059] In other embodiments, since nitrogen gas heats up after compression, it is cooled via heat exchanger 220 to maintain stable operating conditions. Nitrogen gas enters through the inlet of heat exchanger 220 and exits through its outlet, where it is cooled by circulating cooling water. In some embodiments, heat exchanger 220 may be a shell-and-tube heat exchanger.
[0060] In existing technologies, nitrogen in a powder nitrogen conveying system is typically pressurized by compressor 210, cooled by heat exchanger 220, and then vented for further processing. This application introduces a branch after heat exchanger 220 to recover and reuse the nitrogen that would otherwise be released into the atmosphere, using it as the working fluid in the degassing section of the extrusion granulator 300, thus powering the ejector fluid in the degassing section. Compared to existing technologies that use a liquid ring vacuum pump to power a vacuum suction system to extract exhaust gases, this application not only eliminates the need for a mechanical power system but also recovers and reuses nitrogen released into the atmosphere, saving energy while also recycling waste gas.
[0061] Therefore, this application connects the first branch 121 downstream of the heat exchanger 220, which can pressurize and cool the nitrogen in the nitrogen pipeline, so that the nitrogen enters the ejector 140 with a higher pressure, thereby forming a jet and generating negative pressure, which facilitates the extraction and accelerated delivery of hydrocarbon gas from the extrusion granulator 300 into the waste gas treatment system 130.
[0062] In some embodiments, the powder nitrogen conveying pipeline is further provided with a second flow regulating valve 230, which is located upstream of the first branch 121. The opening degree of the second flow regulating valve 230 can be 0%, 11%, 15%, 22%, 25%, 28%, 30%, 35%, 42%, 48%, 50%, 58%, 65%, 70%, 85%, 90%, or 100%. That is, the nitrogen flow rate of the powder nitrogen conveying pipeline can be adjusted upstream of the first branch 121 via the second flow regulating valve 230.
[0063] Through the above embodiments, this application has the following beneficial effects or advantages: 1) This application utilizes a closed-loop nitrogen conveying system 200 for powder production, providing a stable gas source as the working fluid. Hydrocarbon gases from the granulator unit are used as the ejector fluid. The ejector fluid and working fluid are mixed and pressurized within the ejector 140 to form a mixed compressed fluid, which is then discharged through the mixed outlet to the waste gas treatment system 130. This achieves the goal of removing hydrocarbon gases emitted from the extrusion granulator section without increasing gas source consumption or mechanical energy consumption, thereby reducing volatile organic compound (VOC) content and product odor, improving production process safety and product market competitiveness. It also reduces the problem of Class A material accumulation that easily occurs with traditional vacuum suction systems, minimizing the impact on surrounding explosion hazard zone classifications and building categories.
[0064] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.
[0065] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", and "counterclockwise" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.
[0066] In this application, unless otherwise expressly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.
[0067] Furthermore, the use of terms such as "first" and "second" in this application is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, features defined with "first" or "second" may explicitly or implicitly include one or more features. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.
[0068] Although embodiments of this application have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the claims and their equivalents.
Claims
1. A waste gas emission system for a polyolefin plant, characterized in that, include: A closed-loop nitrogen conveying system for powder materials is equipped with an exhaust end; Extrusion granulation unit, used to remove hydrocarbon gases; The exhaust gas branch has an exhaust gas branch inlet and an exhaust gas branch outlet, wherein the exhaust gas branch inlet is connected to the hydrocarbon gas removed from the extrusion granulation unit; The power branch includes a first branch, which has a first branch inlet and a first branch outlet. The first branch inlet is used to connect with the exhaust end of the powder nitrogen conveying system. The exhaust gas treatment system is equipped with an exhaust gas treatment inlet; The injector is provided with a first inlet connected to the exhaust gas branch outlet, a second inlet connected to the first branch outlet, and a mixing outlet connected to the exhaust gas treatment inlet. In this system, the gas source at the exhaust end of the powder nitrogen conveying system is mixed with the hydrocarbon gas from the waste gas branch in the injector, so as to draw and pressurize the hydrocarbon gas from the mixing outlet of the injector and discharge it to the waste gas treatment system.
2. The exhaust gas emission system in the polyolefin plant according to claim 1, characterized in that, The power branch includes a first flow-limiting orifice plate disposed on the first branch, the first flow-limiting orifice plate being located upstream of the second inlet of the injector.
3. The exhaust gas emission system in the polyolefin plant according to claim 2, characterized in that, The power branch also includes an exhaust branch connected in parallel with the first branch. The exhaust branch is equipped with a first flow regulating valve. The inlet of the exhaust branch is used to connect with the exhaust end of the powder nitrogen conveying system, and the outlet of the exhaust branch is connected with the exhaust gas treatment inlet of the waste gas treatment system.
4. The exhaust gas emission system in the polyolefin plant according to claim 3, characterized in that, The first branch is also equipped with a pressure transmitter, which is located upstream of the first flow-limiting orifice plate.
5. The exhaust gas emission system in the polyolefin plant according to claim 4, characterized in that, The exhaust gas system in the polyolefin plant also includes a controller, which is signal-connected to the pressure transmitter and the first flow regulating valve.
6. The exhaust gas emission system in a polyolefin plant according to any one of claims 1-5, characterized in that, The power branch also includes a nitrogen source and a second branch connected to the nitrogen source; The second branch is connected in parallel with the first branch, and the second branch is connected to the second inlet of the injector.
7. The exhaust gas emission system in the polyolefin plant according to claim 6, characterized in that, The power branch also includes a second flow limiting orifice plate and a switching valve disposed on the second branch. The second flow limiting orifice plate is located downstream of the switching valve and upstream of the injector.
8. The exhaust gas emission system in a polyolefin plant according to any one of claims 1-5, characterized in that, The exhaust gas treatment system also includes a connecting pipe and a one-way valve disposed on the connecting pipe, the connecting pipe being located between the mixing outlet of the injector and the exhaust gas treatment system.
9. The exhaust gas emission system in a polyolefin plant according to any one of claims 1-5, characterized in that, The exhaust gas branch also includes a condenser body, which has a cooling water inlet, a cooling water outlet, a gas phase inlet, and a gas phase outlet. The gas phase inlet of the condenser body is used to communicate with the hydrocarbon gas removed from the extrusion granulator unit, and the gas phase outlet of the condenser body is connected to the first inlet of the ejector.
10. The exhaust gas emission system in a polyolefin plant according to any one of claims 1-5, characterized in that, The exhaust gas treatment system includes at least one of a low-pressure flare, an RTO system, a VCU system, and a CEB system.
11. The exhaust gas emission system in a polyolefin plant according to any one of claims 1-5, characterized in that, The injector also includes: A receiving chamber, wherein the receiving chamber is equipped with a nozzle; The mixing chamber is in communication with the nozzle; and, The diffuser is connected to both the mixing chamber and the exhaust gas treatment system. The first inlet and the second inlet are located in the receiving chamber, and the mixing outlet is located in the diffuser.
12. The exhaust gas emission system in the polyolefin plant according to claim 11, characterized in that, The powder nitrogen delivery system includes a powder nitrogen delivery pipeline connected to the nitrogen pipeline, a compressor and a heat exchanger installed in the powder nitrogen delivery pipeline. The inlet of the compressor is connected to the nitrogen pipeline, the outlet of the compressor is connected to the inlet of the heat exchanger, and the outlet of the heat exchanger is connected to the first branch of the exhaust gas emission system.
13. The exhaust gas emission system in the polyolefin plant according to claim 12, characterized in that, The nitrogen conveying pipeline for the powder is also equipped with a second flow regulating valve, which is located upstream of the first branch.