Process optimization and equipment selection of polyester resin production units for powder coatings

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Powder coating is a coating with 100% solid content and painted in powder form.
Its biggest advantage is that it does not require the use of organic solvents or water as a dispersion medium.
Therefore, it has no solvent volatilization during use, is safe and environmentally friendly, and conforms to the internationally recognized "4E" rule: Economical, Environmental, Effectiveness and Excellence [1], becoming a market com" href="http://">Online coatingol.
com is the most popular paint variety .
The polyester resin is the most important and the largest proportion of polyester powder coatings.
In recent years, its market scale has grown rapidly.

China’s "Polyester Factory Design Specification" [2] stipulates the technical requirements for polyester factory design, but the specification applies to the use of terephthalic acid and ethylene glycol as raw materials to produce ethylene terephthalate.

Starting from the actual design experience of a certain polyester production plant, this article introduces the process optimization experience and the selection of main equipment for the reference of engineering designers.

1 Process flow introduction

The main production process of polyester resin for powder coatings is made from terephthalic acid, isophthalic acid, and neopentyl glycol as the main raw materials, through heating esterification reaction and vacuum dehydration polycondensation.
The polyester resin production device mainly includes five processes including ingredient feeding, heating and esterification, polycondensation dehydration, cooling and crushing, and packaging and warehousing.
The schematic diagram of the process flow is shown in Figure 1.

Generally speaking, the polyester resin production device adopts a single-kettle process and intermittent operation.

2 Process optimization

2.
1 Process optimization

The project owner intends to expand production capacity and build a new 80,000t/a production device.
If a production line with a production capacity of 5500t/a is used, it will need to arrange as many as 15 production lines, which is obviously uneconomical.

According to analysis, a single batch of 32h is mainly composed of the following steps: initial feeding 1.

By shortening the feeding and discharging time, the production capacity can only be increased by less than 10%, which is obviously difficult to meet the requirements.

In summary, by shortening the production time of a single batch, the production capacity of the 30m³ reactor can be increased from 5500t/a to 11700t/a, an increase of 112%.

The enlargement of the reactor is a very complicated problem.

By enlarging the volume of the reactor, the production capacity of a single batch can be increased by 23%.

2.

In conventional polyester resin production equipment for powder coatings, the reactor usually uses open feeding.

In order to solve the problem of opening the lid and feeding, this project adopts a closed design for the pre-polymerization kettle and the final polymerization kettle, that is, during the entire production process, there is no need to open the feeding hole or manhole.

2.
3 Equipment selection

The main equipment of this project adopts the existing mature equipment types of the owner, but there are certain innovations in the selection of some equipment to meet the requirements of expanding production capacity, increasingly strict safety, environmental protection and reducing labor intensity of workers.

Pipe chain conveyor is a continuous conveying equipment for conveying bulk materials such as powder and small particles, and is widely used in the polyester fiber industry.
The pipe chain conveyor is composed of the pipeline, the chain and scraper inside the pipeline, the driving wheel and the passive wheel, and the horizontal and vertical movement of the solid material is realized by the rotation of the chain and the scraper.
In this project, three pipe chain conveyors are selected for terephthalic acid and isophthalic acid respectively to realize the horizontal-vertical-horizontal transportation of the two materials from the warehouse to the polyester workshop, and finally discharge the materials to the feeding bin.
At the same time, terephthalic acid is also equipped with a 1,000m³ raw material warehouse and a set of supporting pipe chain conveyors for feeding.
The terephthalic acid is sealed and fed to the pipe chain machine by a tanker and vertically transported to the raw material warehouse.
In this process, the material runs in a closed equipment to avoid the escape of dust to the greatest extent.

The vacuum feeder uses a vacuum pump or compressed air and nitrogen as power, and is composed of a membrane filter bag filter, a compressed air blowback device, a pneumatic discharge door device, a vacuum hopper, a stainless steel suction gun, and a delivery hose.
The vacuum hopper is connected with the reaction kettle by a flange, and a small amount of solid materials are sucked into the vacuum hopper through negative pressure and discharged into the reaction kettle.
The entire operation process is fast and reliable, prevents dust pollution, and realizes the closed operation of the reactor.

3 Conclusion

(1) The production capacity of a single production line of polyester resin for powder coatings was successfully increased from 5500t/a to 14,400t/a through the process optimization measures of changing the batch operation of single tank to semi-continuous operation of double tank and the low-scale amplification of the reactor.

(2) The use of tube chain conveyor and vacuum feeder equipment can realize the large and small batch feeding of solid materials respectively, so that the polyester reactor can be operated in a completely closed state, and dust escape and high-temperature steam volatilization are avoided.
Improve the workshop environment.