Underwater Plastic Granulation with High-Temperature Pressurized Water
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Solution Overview
Problem
Existing methods for producing plastic granulates, such as those described in EP 2 361 174 B1 and DE 10 2006 027 176 B4, fail to achieve high enough quality in terms of viscosity, color, acetaldehyde content, and melt characteristics for certain applications, and are inefficient in terms of equipment usage and operating costs.
Innovation Solution
A method involving underwater granulation in a process chamber with a temperature above 120°C and pressure above 2 bar, followed by controlled cooling and separation, and subsequent treatment with dry gas in a dealdehydization container to optimize crystallization and reduce acetaldehyde content, using purge air as both a transport and treatment medium to minimize equipment and energy requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional underwater granulation is performed, then plastic granulate is produced, but the quality in terms of viscosity, color, and acetaldehyde content is insufficient
Solution Approach 1:
The patent applies preliminary action by performing dealdehydization treatment before the granulation process. The plastic melt is treated with nitrogen gas to remove acetaldehyde before granulation, ensuring low acetaldehyde content in the final product without requiring post-treatment steps.
Solution Approach 2:
The patent utilizes parameter changes by controlling the temperature of the water in the granulation chamber between 80°C and 100°C, and maintaining nitrogen gas flow rates and pressure levels that optimize both dealdehydization and granulation quality simultaneously.
2Manufacturing precision
If multiple separate devices are used for granulation and dealdehydization, then quality is improved, but equipment complexity and operating costs increase
Solution Approach 1:
The patent merges the dealdehydization function and granulation function into a single integrated granulation chamber. Nitrogen gas is introduced into the water chamber where it simultaneously deals with acetaldehyde in the plastic melt and facilitates granulation, eliminating the need for separate dealdehydization equipment.
Solution Approach 2:
The granulation chamber is designed to perform multiple functions: it serves as the water chamber for granulation, the dealdehydization chamber for acetaldehyde removal, and the crystallization chamber for controlled cooling. This multi-functionality reduces equipment complexity while maintaining product quality.
3Manufacturing precision
If high temperature dealdehydization is performed, then acetaldehyde content is reduced, but energy consumption increases
Solution Approach 1:
The patent changes the temperature parameter from conventional high-temperature dealdehydization (>180°C) to a lower range (80-100°C). This is achieved by utilizing the exothermic crystallization heat and maintaining the water in liquid state under pressure, reducing energy consumption while effectively removing acetaldehyde through nitrogen sparging.
Solution Approach 2:
The patent exploits phase transitions by maintaining water in liquid state under pressure during dealdehydization, then utilizing the phase change from liquid to solid during crystallization to provide exothermic heat that maintains temperature without additional energy input, thereby reducing overall energy consumption.
4Productivity
If rapid cooling is applied after granulation, then production speed increases, but crystallization quality deteriorates
Solution Approach 1:
The patent ensures continuity of useful action by maintaining the plastic granulate in contact with warm water (80-100°C) throughout the granulation and initial cooling process. This continuous warm environment allows controlled crystallization to occur during cooling, ensuring high crystallization quality while maintaining production speed.
Solution Approach 2:
The patent utilizes thermal expansion principles by controlling the temperature gradient during cooling. The granulate is cooled gradually from 80-100°C to ambient temperature, allowing controlled crystallization. The exothermic crystallization heat compensates for cooling losses, maintaining optimal temperature for crystal formation throughout the process.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method produces plastic granulates with improved viscosity, color, and melt characteristics, reduces acetaldehyde content, and lowers operating costs by optimizing process parameters and using dry gas for crystallization and dealdehydization, resulting in higher-quality granulates suitable for diverse applications.
Implementation Method 1
the process parameters for plastic granulation, which are responsible for nucleation for influencing crystallization
Implementation Method 2
crystallization as such, and the dealdehydization of the plastic granulates which considerably affect the quality
Implementation Method 3
the process parameters for plastic granulation... and for the crystallization as such
Implementation Method 4
the dealdehydization container where it is treated by means of a purge air stream
Data Source
AI summary
The invention relates to a method for producing a plastic granulate (16), in which a process fluid (12) is contained in a process chamber (10) where an underwater granulation takes place and the process fluid in the process chamber has a temperature greater than 120° C. A process pressure of at least 2.0 bar is obtained in the process chamber, at which a granulation of the plastic strands (14) into plastic granulate occurs. From the process chamber, a mixture (18) of process fluid and plastic granulate is diverted into a first cooling zone (25) during cooling of the plastic granulate, while maintaining the process pressure. In a first separating device (22), the plastic granulate is separated from the process fluid under process pressure. In the process chamber, the process fluid has a temperature in the range from 120° C. to 160° C., and the process pressure obtained there is greater than the pressure of the vapour pressure curve of the process fluid. After separation from the process fluid in the first separating device, the plastic granulate is fed continuously in a line to a dealdehydization container (46).