Olefin Polymerization Heat Exchanger Fouling Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Fluidised bed polymerisation processes for olefins in reactors experience significant fouling due to the entrainment of fine particles, leading to frequent shutdowns for cleaning of heat exchangers and other equipment, despite the use of disengagement chambers and gas/solid separators.
Innovation Solution
A process and apparatus for gas-phase polymerisation in a fluidised bed reactor that includes a gas/solids separator to remove solid particles from the gaseous stream, allowing residual particles to contact heat exchangers, maintaining high heat transfer efficiency and minimizing fouling by controlling particle size and velocity, thereby reducing pressure drop and heat transfer degradation over time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a disengagement chamber and gas/solid separator are used to remove entrained particles, then particle removal efficiency is improved, but fine particles still foul heat exchangers and equipment
Solution Approach 1:
The patent introduces a liquid stream as an intermediary substance that contacts the gaseous olefin stream containing fine particles before it reaches the heat exchanger. This liquid stream captures and removes the fine particles through absorption or adhesion, preventing them from depositing on the heat exchanger surfaces. The liquid acts as a mediator between the particle-laden gas and the heat exchanger, solving the fouling problem while maintaining particle removal efficiency.
Solution Approach 2:
The patent changes the physical state and composition parameters of the gas stream by introducing a liquid phase. This parameter change transforms the single-phase gaseous stream into a two-phase liquid-gas system, where the liquid phase selectively interacts with and removes fine particles. The modification of stream parameters (adding liquid, changing composition) prevents particle deposition on heat exchangers.
2Temperature
If the recycle stream is cooled to condense liquid for reintroduction into the reactor, then heat of reaction is removed, but significant quantities of heat are consumed by vaporisation
Solution Approach 1:
The patent converts the harmful effect of fine particle entrainment (which causes fouling) into a beneficial outcome. By allowing fine particles to pass through the heat exchanger in a controlled environment where they don't deposit, the system eliminates the need for energy-intensive cleaning operations and maintains continuous operation. The fine particles, rather than being seen as a problem to be completely eliminated, are managed in a way that converts potential harm into operational benefit.
Solution Approach 2:
The patent extracts the fine particle removal function from the traditional gas/solid separator and relocates it to a liquid contactor system. Instead of attempting to remove all particles before the heat exchanger, the system extracts only the problematic fine particles that would cause fouling, while allowing larger particles to be handled by the existing separation equipment. This selective extraction approach reduces energy consumption while maintaining effectiveness.
3Reliability
If gas velocity is reduced in the disengagement chamber, then particle entrainment is minimized, but residence time increases and productivity decreases
Solution Approach 1:
The patent segments the particle removal function into multiple stages: coarse particle removal in the disengagement chamber at higher velocities, fine particle removal in the liquid contactor, and final separation before the heat exchanger. This segmentation allows each stage to operate at optimal velocities for its specific particle size range, maintaining short residence time while effectively removing particles of all sizes.
Solution Approach 2:
The patent uses hydraulic principles by introducing a liquid stream to capture fine particles. The liquid-gas two-phase flow system utilizes fluid dynamics to separate and remove particles without requiring long residence times. The hydraulic action of the liquid stream efficiently captures particles in a compact volume, maintaining high productivity while controlling entrainment.
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
The process achieves negligible fouling rates, allowing continuous operation for years without cleaning heat exchangers, with heat exchanger efficiency maintained above 650 W/m2/°C and pressure drop increase limited to less than 5% per year, enabling extended plant operation without shutdowns.
Implementation Method 1
the recycling loop to comprise at least one gas/solid separator, preferably a cyclone, capable of separating, from the gas stream, a substantial portion of the solid particles entrained within it
Implementation Method 2
the expansion of which causes a reduction in the velocity of the ascending gas stream above the fluidised bed and which allows entrained particles to fall back into the fluidised bed
Implementation Method 3
the process comprises a recycling loop by which the ascending gas stream withdrawn at the top part of the reactor is recycled to the base. Further, since the polymerisation reaction is highly exothermic the recycling stream is generally cooled to remove the heat of reaction
Implementation Method 4
Current commercial operation generally prefers that the recycle stream is cooled such that a portion thereof condenses to form liquid
Implementation Method 5
The polymerisation of olefin monomers in the presence of catalysts in fluidised bed reactors is well-known
Implementation Method 6
since the polymerisation reaction is highly exothermic the recycling stream is generally cooled to remove the heat of reaction
Implementation Method 7
An industrially favoured process employs a fluidisation grid to distribute the fluidising gas to the bed
Data Source
AI summary
Process for the gas-phase polymerization of olefins in a fluidized bed reactor, by a) passing a fluidizing gas containing an olefin monomer through a fluidized bed of polymer particles in the presence of a polymerization catalyst, b) withdrawing a first gaseous stream containing solid particles from the reactor, c) passing the first gaseous stream to a gas/solids separator, separating solid particles, and forming a second gaseous stream containing residual solid particles, d) passing a portion of the second gaseous stream to a heat exchanger(s) to remove heat and e) recycling a portion of the cooled stream from (d) as the fluidizing gas in (a). The fouling rate of the heat exchanger (s) is such that i) the increase in pressure drop across the heat exchanger is equivalent to less than 5%/year, and/or ii) the decrease in heat transfer of the heat exchanger is equivalent to less than 5%/year.