A green low-pollution coating system

Abstract

The present application belongs to the technical field of atmospheric pollution control, and specifically relates to a green low-pollution coating system. The present application realizes green low-pollution coating through closed-loop recycling of carbon dioxide and VOCs, and the structure comprises a supercritical CO2 spraying system, a paint mist filtering unit, a VOCs adsorption unit, a CO2 absorption unit, a vacuum desorption unit, a pressurization and temperature rising unit and a desorption fluid (CO2+VOCs) recycling pipeline system connected in sequence, namely, the desorption fluid (CO2+VOCs) enters the supercritical CO2 spraying system through the recycling pipeline. The supercritical CO2 spraying system is composed of a supercritical CO2 generating system, a coating conveying system, a coating mixing system and a spraying system. The present application can reduce the amount of VOCs generated in the spraying process, recycle carbon dioxide, realize near-zero emission of VOCs and carbon dioxide, achieve the goal of greenization and low-pollution of the coating process, and is conducive to the popularization and application of supercritical CO2 fluid spraying technology.

Description

Technical Field

[0001] This invention belongs to the field of air pollution control technology, specifically relating to a green and low-pollution coating system. Background Technology

[0002] The coatings used in the painting industry contain a large amount of organic solvents. These solvents evaporate and dissipate during storage and spraying, ultimately forming volatile organic compounds (VOCs) pollution. This makes the painting industry a key area for VOCs emission reduction. VOCs not only contribute to photochemical smog and haze, polluting the environment, but also harm human health. The government has successively introduced relevant laws and regulations to restrict the use and emission of VOCs, thereby guiding and promoting the painting industry's transformation towards green and low-pollution spraying.

[0003] Traditional air spraying requires large amounts of organic solvents to dilute the materials, resulting in low coating efficiency, poor paint utilization, and the generation of significant VOCs during the spraying process, leading to paint waste. Compared to traditional spraying technologies, supercritical CO2 spraying can replace some of the volatile organic solvents in the paint with supercritical CO2 fluid, reducing the amount of organic solvent used and thus significantly lowering the VOCs generated during the spraying process. This effectively protects the environment, reduces pollution, and represents a green spraying technology. Currently, domestic patents CN 201811465806.2 and CN201721789891.9 both propose a VOCs-free spraying process that uses supercritical CO2 to replace organic solvents in traditional spraying. Japanese company Nagase Sangyo Co., Ltd.'s patent CN201980038076.4 proposes a coating apparatus and method that mixes CO2 and paint, maintaining CO2 in a liquid state for stable spraying. Although the above process replaces some of the solvents in the coating, in practical applications, due to the need to reduce the viscosity of the coating, some organic solvents will inevitably be added, making it impossible to achieve true zero VOC emissions, and carbon dioxide emissions will also be emitted. Summary of the Invention

[0004] To address the above problems, this invention provides a green and low-pollution coating system to reduce VOC emissions.

[0005] This invention utilizes supercritical CO2 as a partial solvent replacement in the coating process, and achieves zero emissions of VOCs generated during the coating process through further purification. At the same time, the emitted CO2 gas and organic solvents are recycled, thus realizing a green and low-pollution coating process.

[0006] The green and low-pollution coating system provided by this invention achieves green and low-pollution coating through closed-loop recycling of carbon dioxide and VOCs. Its structure includes, in sequence, a supercritical CO2 spraying system, a paint mist filtration unit, a VOCs adsorption unit, a CO2 absorption unit, a vacuum desorption unit, a pressurization and heating unit, and a desorption fluid (CO2+VOCs) recycling pipeline system. Specifically, the desorption fluid (CO2+VOCs) enters the supercritical CO2 spraying system through the recycling pipeline; wherein:

[0007] The supercritical CO2 spraying system comprises a supercritical CO2 generation system, a paint delivery system, a paint mixing system, and a spraying system. (See attached image.) Figure 2 As shown in the diagram. The supercritical CO2 generation system includes a CO2 cylinder, a shut-off valve 1, a CO2 cooler, a pressurized gas supply pump, and a CO2 heater connected in sequence; the paint delivery system includes a paint tank, a shut-off valve 2, a paint pressurized delivery pump, and a paint heater connected in sequence; the paint mixing system includes a temperature control system, a mixing vessel, and a shut-off valve 3 connected in sequence, with the temperature in the mixing vessel controlled by the temperature control system; the spraying system includes an adjustable spray nozzle and a spray gun; the inlet of the adjustable spray nozzle is connected to the outlet of the shut-off valve 3 via a pipe, and the outlet of the adjustable spray nozzle is connected to the spray gun via a pipe.

[0008] In the supercritical CO2 spraying system, CO2 originates from a CO2 cylinder or a desorption fluid (CO2+VOCs) recycling pipeline system. After passing through shut-off valve 1, a CO2 cooler, a pressurized gas pump, and a CO2 heater, it enters the mixing vessel of the paint mixing system. The paint, originating from the paint tank, also enters the mixing vessel of the paint mixing system via shut-off valve 2, a paint pressurized delivery pump, and a paint heater. CO2 and paint are mixed in the mixing vessel, and after the temperature is controlled by a temperature control system, the mixture is sprayed out through shut-off valve 3, the adjustable nozzle of the spraying system, and the spray gun. The CO2, VOCs, and paint mist emitted after the paint is sprayed are collected and enter the paint mist filtration unit of a closed-loop carbon dioxide and VOCs recycling system. This process is repeated to achieve the reuse of CO2 and VOCs.

[0009] The supercritical CO2 spraying system has a pressure range of 5–12 MPa and a temperature range of 30–70 °C.

[0010] The paint mist filtration unit can be configured with multiple stages to intercept organic solvents added to reduce the viscosity of the coating and carbon dioxide used to replace some of the solvents, as well as paint mist, in the exhaust gas emitted from the coating system.

[0011] The VOCs adsorption unit, composed of zeolite or activated carbon, is used to selectively adsorb VOCs from gaseous pollutants filtered by the paint mist filtration unit.

[0012] The carbon dioxide adsorption unit uses a molecular sieve adsorption material that adsorbs CO2 to adsorb CO2-containing gas that has been treated by the VOCs adsorption unit; the clean gas is discharged directly.

[0013] The vacuum desorption unit desorbs, pressurizes, and heats the CO2 adsorbed by the carbon dioxide adsorption unit, turning it into a supercritical fluid that is returned to the VOCs adsorption unit. The VOCs enriched in the VOCs adsorption unit are then extracted using supercritical carbon dioxide. The extracted carbon dioxide fluid, mixed with volatile organic compounds, is returned to the supercritical carbon dioxide generation system and recycled as a solvent for the coating in the spraying system. This forms a closed-loop cycle, reusing CO2 and organic solvents to achieve near-zero emissions.

[0014] The specific process is as follows: The exhaust gas emitted from the coating system contains organic solvents added to reduce the viscosity of the paint, carbon dioxide used to replace some of the solvents, and paint mist. After collection, the paint mist in this exhaust gas is trapped by a multi-stage paint mist filtration unit. The filtered gaseous pollutants enter a VOCs adsorption unit composed of zeolite or activated carbon, where VOCs in the gas are selectively adsorbed. The treated gas containing CO2 passes through a dedicated carbon dioxide adsorption unit, where CO2 is enriched by a specialized molecular sieve adsorption material. The clean gas is directly discharged. The CO2 is then desorbed, pressurized, and heated by a vacuum desorption unit to become a supercritical fluid, which is returned to the VOCs adsorption system. The VOCs enriched in the VOCs adsorption unit are then subjected to supercritical carbon dioxide extraction. The extracted carbon dioxide fluid mixed with volatile organic compounds is returned to the supercritical carbon dioxide generation system and recycled back into the spraying system as a solvent for the paint. This forms a closed-loop cycle, reusing CO2 and organic solvents to achieve near-zero emissions.

[0015] The main advantages of this invention are:

[0016] (1) This invention not only uses carbon dioxide to replace some of the volatile organic solvents in the spraying process, reducing the amount of VOCs generated during the spraying process, but also uses a special carbon dioxide adsorbent to recycle carbon dioxide and reduce carbon emissions.

[0017] (2) The recovered carbon dioxide is pressurized and used as an extractant to desorb VOCs in the VOCs adsorption unit.

[0018] (3) This invention can reuse VOCs and carbon dioxide generated during the coating process, achieving near-zero emissions and achieving the goals of greening and low pollution in the coating process, which is conducive to the promotion and application of supercritical CO2 fluid spraying technology. Attached Figure Description

[0019] Figure 1This is a structural diagram of the green and low-pollution coating system of the present invention.

[0020] Figure 2 This is a structural diagram of a supercritical CO2 spraying system. Detailed Implementation

[0021] Figure 1 This is a structural diagram of the green and low-pollution coating system of the present invention, namely a closed-loop recycling system for carbon dioxide and VOCs. Figure 2 This is a system flow diagram of a supercritical CO2 spraying system.

[0022] The present invention will be further described in detail below with reference to the accompanying drawings and through embodiments. The following embodiments are explanations of the present invention, but the present invention is not limited to the following embodiments.

[0023] like Figure 1 As shown, a green, low-pollution coating system includes a supercritical CO2 spraying system, a multi-stage paint mist filtration system, an adsorption system, an exhaust system, a CO2 absorption system, a CO2 desorption system, and a paint circulation system. The supercritical CO2 spraying system, as shown... Figure 2 As shown, it consists of a supercritical CO2 generation system, a coating delivery system, a coating mixing system, and a spraying system. On one hand, CO2 stored in a gas cylinder is liquefied by a CO2 cooler, then pressurized to 7 MPa by a high-pressure CO2 pump, and then heated to 35°C by a CO2 heater before being supplied to the mixing system. On the other hand, a mixture of acrylic resin and organic solvents such as acetone and ethyl acetate stored in a coating tank is pressurized to 7 MPa by a coating pressurization pump, then heated to 33°C by a coating heater before being supplied to the mixing system. Next, the mixture in the mixing vessel is pressurized, and the temperature control system maintains the temperature in the mixing vessel at approximately 34°C. The shut-off valve 3 opens, and supercritical CO2 carrying the coating flows out of the mixing vessel, spraying through an adjustable nozzle and a spray gun with small orifices. The coating is atomized by the supercritical CO2, depressurized to atmospheric pressure, and then uniformly sprayed onto the substrate surface to form a coating film. The CO2 instantly vaporizes and evaporates, automatically separating from the coating components along with the organic solvents in the coating, and entering the exhaust gas collection system. The adjustable nozzle inlet is connected to the outlet of shut-off valve 3 via a pipe, and the adjustable nozzle outlet is connected to the spray gun via a pipe. The temperature inside the mixing tank is controlled by a temperature control system. This method allows for coating and printing on the workpiece. The performance of the sprayed coating meets relevant national standards.

[0024] Because organic solvents are added to reduce the viscosity of the coating, VOCs generated during the spraying process need to be purified. The sprayed gas enters a multi-stage paint mist filtration system, which traps particulate matter. The filtered gaseous pollutants then enter an adsorption unit composed of zeolite, where VOCs are selectively adsorbed. The treated gas containing CO2 passes through a molecular sieve adsorption material to enrich the CO2, and the clean gas is discharged directly. The CO2 undergoes vacuum desorption, pressurization to 7 MPa, and heating to 32°C to become a supercritical fluid, which is then recycled in the VOCs adsorption unit for supercritical extraction of organic matter. The extracted carbon dioxide fluid containing volatile organic compounds is returned to the supercritical CO2 spraying system and connected to the shut-off valve 1 of the supercritical CO2 generation system, where it is reused as a solvent in the coating system, thus forming a closed-loop cycle that reuses both CO2 and organic solvents.

Claims

1. A green, low-pollution coating system, characterized in that, A green and low-pollution coating process is achieved through closed-loop recycling of carbon dioxide and VOCs. Its structure includes a supercritical CO2 spraying system, a paint mist filtration unit, a VOCs adsorption unit, a carbon dioxide adsorption unit, a vacuum desorption unit, a pressurization and heating unit, and a CO2+VOCs desorption fluid recycling pipeline system, wherein the CO2+VOCs desorption fluid enters the supercritical CO2 spraying system through the recycling pipeline; wherein: The supercritical CO2 spraying system comprises a supercritical CO2 generation system, a paint delivery system, a paint mixing system, and a spraying system. The supercritical CO2 generation system includes, in sequence, a CO2 cylinder, a first shut-off valve, a CO2 cooler, a pressurized gas supply pump, and a CO2 heater. The paint delivery system includes, in sequence, a paint tank, a second shut-off valve, a paint pressurized delivery pump, and a paint heater. The paint mixing system includes, in sequence, a temperature control system, a mixing vessel, and a third shut-off valve; the temperature inside the mixing vessel is controlled by the temperature control system. The spraying system includes an adjustable spray nozzle and a spray gun. The inlet of the adjustable spray nozzle is connected to the outlet of the third shut-off valve via a pipe, and the outlet of the adjustable spray nozzle is connected to the spray gun via a pipe. The paint mist filtration unit is configured with multiple stages to intercept organic solvents added to reduce the viscosity of the paint and carbon dioxide used to replace some of the solvents in the exhaust gas emitted from the coating system, as well as paint mist in the paint mist. The VOCs adsorption unit is composed of zeolite or activated carbon and is used to selectively adsorb VOCs from gaseous pollutants filtered by the paint mist filtration unit. The carbon dioxide adsorption unit uses a molecular sieve adsorption material that adsorbs CO2 to adsorb CO2-containing gas that has been treated by the VOCs adsorption unit; the clean gas is discharged directly. The vacuum desorption unit desorbs, pressurizes, and heats the CO2 adsorbed by the carbon dioxide adsorption unit, turning it into a supercritical fluid that is returned to the VOCs adsorption unit. The VOCs enriched in the VOCs adsorption unit are then extracted using supercritical carbon dioxide. The extracted carbon dioxide fluid, mixed with volatile organic compounds, is returned to the supercritical carbon dioxide generation system and recycled as a solvent for the coating in the spraying system. This forms a closed-loop cycle, reusing CO2 and organic solvents to achieve near-zero emissions.

2. The green and low-pollution coating system according to claim 1, characterized in that, In the supercritical CO2 spraying system, CO2 originates from a CO2 cylinder or a CO2+VOCs desorption fluid recycling pipeline system. After passing through a first shut-off valve, a CO2 cooler, a pressurized gas supply pump, and a CO2 heater, it enters the mixing vessel of the paint mixing system. The paint, originating from a paint tank, also enters the mixing vessel of the paint mixing system after passing through a second shut-off valve, a paint pressurized delivery pump, and a paint heater. CO2 and paint are mixed in the mixing vessel of the paint mixing system, and after the temperature is regulated by a temperature control system, the mixture is sprayed out through a third shut-off valve, an adjustable spray nozzle, and a spray gun of the spraying system. After the paint is sprayed out, the CO2, VOCs, and paint mist that are emitted are collected and enter the paint mist filtration unit of the carbon dioxide and VOCs closed-loop recycling system. The above operation is repeated to achieve the reuse of CO2 and VOCs.

3. The green and low-pollution coating system according to claim 2, characterized in that, The supercritical CO2 spraying system has a pressure range of 5~12MPa and a temperature range of 30~70℃.

4. The green and low-pollution coating system according to claim 1, characterized in that, The workflow is as follows: The exhaust gas from the coating system contains organic solvents added to reduce paint viscosity, carbon dioxide used to replace some solvents, and paint mist. This exhaust gas is collected and filtered by a multi-stage paint mist filtration unit to trap the paint mist and other pollutants. The filtered gaseous pollutants then enter a VOCs adsorption unit for selective adsorption of VOCs. After treatment, the gas containing CO2 passes through a carbon dioxide adsorption unit to enrich the CO2, and the clean gas is directly discharged. After being analyzed, pressurized, and heated in the vacuum desorption unit, it becomes a supercritical fluid and returns to the VOCs adsorption unit. The VOCs enriched in the VOCs adsorption unit are then subjected to supercritical carbon dioxide extraction. The extracted carbon dioxide fluid mixed with volatile organic compounds is returned to the supercritical carbon dioxide generation system and recycled as a solvent for the coating in the spraying system.

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