International Process Plants. SSP4 Information

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Arthur Wright
5 years ago
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1 International Process Plants SSP4 Information

2 Plant Overview Year Built: 2002 Capacity: 95,000 tons/year Technology: Buehler

3 Table of Contents 1 Process Description 1.1 Process Description: SSP Process for Bottle Grade Resin System Description: Crystallization with Air System Description: Annealing System Description: SSP Reaction System Description: Nitrogen Purification System System Description: Polymer Cooling System Description: Conveyor from Annealer to Reactor System Description: Control and Power System 1.2 SSP Process flow diagram, for reference only SSP Equipment List Photos

4 Process Description 1.1 Process Description: SSP Process for Bottle Grade Resin Solid State Polycondensation Process The solid-state polycondensation process (SSP) is required to upgrade amorphous PET precursor to high quality bottle grade resin that meets the regulations of the authorities and requirements of the packing industry. The most important quality aspects of bottle grade polymer are: Molecular weight: increased in the SSP process to the desired level Acetaldehyde content: decreased in SSP to less than 1ppm Color L*, a8, b8; influenced by polymer recipe, MPP and SSP AA generation in injection molding: polymer recipe, MPP, SSP SSP is a diffusion-controlled process. The main design parameters are temperature and residence time. Both, IV build up as well as AA removal require process temperatures well above 200 C and hold up times in the range of 8 to 12 hours. The polymer needs to be crystallized and dried prior to SSP. Typically the resin is cooled down after the process in order to allow storage and shipping without any impact on product properties.

5 Process Description

6 Process Description System Description: Crystallization with Air The amorphous polymer passes through primary crystallization when it is heated above 130 C. During this process a significant amount of exothermic heat is released which causes a tendency of pellet agglomeration. The crystallization system is designed to avoid such agglomerate formation. The co-monomer content of the polymer has an important impact on the crystallization behavior. Highly modified resins crystallize at a lower rate. Therefore the design of the crystallization system has to be adapted to the polymer recipe. Features of Buhler s Crystallization System: One stage process with a multiple chamber fluid bed heat exchanger. The resin is heated in the multiple chamber fluid bed where also the majority of the primary crystallization is taking place. Agglomeration of pellets is avoided due to the heavy turbulence in the first chamber of the crystallizer. No mechanical agitation and therefore no pellet deformation Crystallization in air environment up to a max. process temp. of 180 C Removal of surface moisture, no hydrolysis (no IV drop) Excellent dedusting of the polymer in the multiple chamber fluid bed heat exchanger Process and equipment patents in conjunction with the crystallization system

7 Process Description System Description: Annealing The crystallized polymer needs to be heated up to the required SSP reaction temperature, which is typically above 200 C. While the resin is heated, it passes through the secondary crystallization stage. This process leads to softening of the pellet surface, which also tends to lead to sintering of the product. The annealing system is designed to avoid sintering of the product. Simultaneously with heating the polymer is dried to very low moisture content. The annealing process is performed in an inert environment, which prevent thermal and oxidative degradation of the resin. Features of Buhler s Annealing System: One stage process in anon-agitated gravity flow reactor with gas cross flow operation. The polymer is gradually heated in several annealing compartments. The moisture is rapidly reduced in the first section of the unit. The secondary crystallization and also a significant amount of reaction take place in the next sections of the annealer. An extremely low bulk pressure and relative movement between the single pellets prevents the polymer from sintering. Approximately 20% of the total molecular weight increase of the process AA level reduced to approximately 5ppm

8 Process Description Gravity flow with excellent residence time distribution No mechanical agitation and therefore no pellet deformation Annealing in inert environment at approx. 220 C (closed N2 loop) No pellet agglomeration, even for highly modified polymers Removal of internal moisture, no hydrolysis (no IV drop) Dedusting of polymer No maintenance required Process and equipment patents in conjunction with the annealing system System Description: SSP Reaction The crystallized and annealed polymer needs to be conditioned in the SSP reactor in order to reach the final specifications. The reaction temperature shall be slightly below the maximum annealing temperature. The residence time is adjusted to reach the required final molecular weight. The secondary crystallization increases slightly during the reaction phase. The reactor is designed to avoid sintering of the product. The reaction process is performed in an inert environment, which prevents thermal and oxidative degradation of the resin.

9 Process Description Features of the Buhler s Reaction System: One stage process in a non-agitated gravity flow reactor with counter current gas flow. The polymer is conditioned at a uniform temperature and a minimal residence time. The reactor is designed to keep the bulk pressure minimized in order to prevent sintering of the polymer. AA level reduced to less than 1ppm Excellent residence time distribution, optimized pellet mass flow characteristics No mechanical agitation and therefore no pellet deformation Reaction in inert environment at 200 C to 225 C (purified N2 loop) Precooling of polymer (<180 C) in the reactor cone No maintenance required Patent on reactor design

10 Process Description System Description: Nitrogen Purification System: The annealer and reactor gas streams collect and eliminate byproducts such as AA, EG, oligomers, dust and water from the SSP reaction. The circulated gas needs to be purified in order to maintain the reaction efficiency of the process and to minimze the nitrogen make up. The SSP reaction requires a process gas with a dew point of less than -30 C, an oxygen level of less than 10 ppm and a hydrocarbon content of less than 10 ppm in order to reach an optimal product quality. Features of Buhler s Gas Purification System: Three stage purification process consisting of filtering, catalytic conversion and gas drying. The process gas streams exiting the annealer and the reactor are combined into one stream and filtered in a common reverse jet filter. The annealer gas is reheated and recycled to the process. The reactor gas is split off and is fully purified in a catalytic converter and dried in a dual desiccant bed. The clean reactor gas is fed back to the reactor at 60 Annealer gas loop with low contamination lever Fully purified reactor gas loop No oxygen in the process gas

11 Process Description Long lifetime of purification system Extremely low maintenance requirements on the purification loop Patent on catalytic converter System Description: Polymer Cooling The solid-state resin needs to be cooled for storage and packaging. The maximum temperature for packaging is typically less than 60 C. Since the polymer temperature exiting the reactor is below 180 C the cooling can be performed in an air environment. Features of the Buhler s Polymer Cooling System: One stage process in a fluid bed cooler The resin is cooled down in a few minutes. Filtered ambient air is used as the cooling medium. There is absolutely no degradation of the polymer due to the quick cooling time and the low pellet inlet temperature. No mechanical agitation and therefore no pellet deformation Cooling in air environment form maximum 180 to 60 C (open air loop) No pellet agglomeration, even for highly modified polymers Excellent dedusting of the polymer

12 Process Description System Description: Conveyor from Annealer to Reactor The polymer exiting the annealer needs to be pneumatically conveyed to the reactor inlet. This intermediate conveying allows optimizing the building layout (height and space requirement) and leads to reduced investment costs. Features of Buhler s Polymer Conveying System: Single stream, low velocity conveying system A closed nitrogen loop connected to the gas purification system is used. The system does not require any make up nitrogen. Very gentle handling of the polymer, no dust generation No additional nitrogen consumption Experience from more than 100 SSP installations System Description: Control and Power System The SSP system includes an independent and flexible control and power system. DCS is from Yokogawa (CS3000). The DC allows operation of the plant form the control room in a fully automated way. Due to the nature of the process, startup and shutdown has to be done by operator intervention.

13 Process Description Features of Proposed Control and Power System: PC operating stations for control and visualization Intelligent software PID controllers Event logging Trending System diagnostics DCS panel Control panel Motor power panels Inverter panels Heating power panels

14 Process Description 1.2 SSP Process flow diagram, for reference only