Dual-Valve Cooling System for Olefin Polymerization Reactor
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Solution Overview
Problem
Existing temperature control methods for gas-phase fluidized-bed reactors used in polyolefin production are inadequate in terms of response time and accuracy, leading to potential oscillations in reactor temperature, which can result in off-spec production, lump formation, fouling, and reactor shutdown, especially for temperature-sensitive catalysts like chromium-based systems.
Innovation Solution
A method involving a cycle gas line with a heat-exchanger cooled by a liquid cooling medium, where the temperature of the cooling medium is controlled by adjusting the flow rate using two continuously operating flow control devices of different sizes connected in parallel, allowing for precise and rapid temperature adjustments within the reactor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single flow control device is used to adjust cooling medium flow rate, then the device structure is simple, but the temperature control precision and response time are insufficient
Solution Approach 1:
The flow control device is segmented into two parallel control valves (first control valve and second control valve) with different flow coefficients. The first control valve handles large flow adjustments while the second control valve handles fine-tuned adjustments, enabling precise temperature control through coordinated operation of multiple segmented components.
2Speed
If the cooling medium flow rate is adjusted rapidly to respond to temperature changes, then the response time is reduced, but the temperature control stability deteriorates
Solution Approach 1:
The system dynamically switches between two control modes based on the magnitude of temperature deviation. For large deviations, the first control valve provides rapid response with large flow adjustments. For small deviations near the setpoint, the second control valve provides fine adjustments to maintain stability, creating a dynamic multi-level control strategy.
Solution Approach 2:
The temperature controller continuously monitors the reactor temperature and provides feedback to adjust the cooling medium flow rate through the two control valves. The feedback mechanism enables automatic correction of temperature deviations while maintaining stability through coordinated valve operation.
3Manufacturing precision
If the reactor temperature is maintained within a narrow window, then the polymerization quality is improved, but the control difficulty increases
Solution Approach 1:
The temperature controller acts as an intermediary that automatically manages the complex control task. It receives temperature feedback, calculates the required cooling adjustment, and coordinates both control valves to achieve the desired temperature maintenance, reducing the operational burden on operators.
Solution Approach 2:
The dual-valve control system with automatic temperature controller enables self-regulating temperature control. The system automatically adjusts cooling medium flow through coordinated valve operation to maintain temperature within the narrow required window, eliminating the need for manual intervention and complex operator decisions.
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 enables precise temperature control within ±0.2°C, improving reactor stability and maintaining the temperature close to the melting point of polyolefins, thus enhancing the polymerization process and reducing the risk of reactor issues.
Implementation Method 1
a heat exchanger for cooling the reactor gas
Implementation Method 2
The withdrawn reactor gas is passed through a heat exchanger and a compressor and then recirculated to the reactor
Data Source
Figure 1
Figure 2
AI summary
A method for controlling the temperature in a polymerization reactor equipped with a cycle gas line for withdrawing reactor gas from the reactor, leading the reactor gas through a heat- exchanger, which is cooled by a cooling medium, which is conveyed in a cooling system through the heat-exchanger, and feeding the reactor gas back to the reactor by adjusting the temperature of the cooling medium entering the heat exchanger, wherein the temperature of the cooling medium entering the heat exchanger is controlled by adjusting the flow rate of the cooling medium in a part of the cooling system by a flow control system comprising two continuously operating flow control devices of different size, which are connected in parallel, a process for polymerizing olefins comprising feeding at least one olefin and at least one polymerization catalyst to a polymerization reactor equipped with a cycle gas line for withdrawing reactor gas from the reactor, leading it through a heat-exchanger for cooling and feeding it back to the reactor, polymerizing the olefins in the presence of the polymerization catalyst and withdrawing the obtained polyolefin from the polymerization reactor, wherein the temperature in the polymerization reactor is controlled by such a method, and a process for controlling the flow rate of a fluid medium by a flow control system comprising two continuously operating flow control devices of different size, which are connected in parallel, wherein the flow control system is controlled by a controller combination comprising a controller controlling the smaller flow control device and a controller controlling the larger flow control device, in which the output of the controller controlling the smaller flow control device is not only fed to the smaller flow control device but also twice to the controller controlling the larger flow control device, once directly as actual value of the controller controlling the larger flow control device and once, after having passed a limiting device, which limits a signal to a centered range, as setpoint of the controller controlling the larger flow control device.