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REACTOR PRODUCTIVITY

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A brief review is made of the different ways available for S-PVC Plants to increase their Productivity and in this way increase Competitiveness.
 
STRATEGIES FOR INCREASING COMPETITIVENESS

To maintain a competitive position, PVC producers have to search permanently for Cost reductions while offering suitable and consistent Quality levels for different applications.
 
Cost Reduction can be done through several Strategies:
 
1) Upstream integration to reduce VCM cost
2) Cutting Conversion Cost and other variable costs
3) Increase Productivity to reduce fixed costs
 
Productivity increase requires a strong knowledge of all phenomena involved in VCM suspension polymerization, since unexpected effects can produce Quality issues and increased Costs from production stoppages, off-spec products, reworks, more Technical service, complaints, reworks, returns, loss of image, etc.
INCREASING PLANT PRODUCTIVITY

PVC Plant Productivity is generally fixed by Polymerization Reactor Productivity (bottleneck) with the rest of equipment having spare capacities.   How much spare capacities determine the amount of investment needed to translate increased Reactor Productivity into Plant Output.

Historically Productivity of PVC Plants has been increased by:
Larger reactor sizes and their automation
 
Pioneered by HÜLS and SHINETSU, this Technology allowed to lower considerably fixed costs by reducing both workforce and construction costs.   Besides, when operating less reactors Productivity increases due to reduction of idle times for occupied systems.
Most S-PVC reactors in operation are around 60 – 150 m3 capacity with Productivities ranging 300 – 550 Ton/m3 year.   VINNOLIT commercializes High-Performance reactors offering 600 – 700 Ton/m3 year but replacing an installed reactor is a huge investment so it is rarely considered for existing plants.
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Reduction of Operating Time (shorter Cycle)
 
Decreases in the polymerization cycle can be made by shortening any operations of the same, such as:
- Charge.- Pumps of higher capacity, simultaneous charges, hot charge, delayed charges, continuous charges.
- Polymerization.- Temperature ramp, final heat-kick, final drop pressure.
- Recovery.- Blow-down, pressure discharge.
- Cleaning/Preparation.- Closed-reactor operation, high-pressure washing, highly efficient antifouling agents
 
However, it is necessary to be careful when any modification is made, taking care to identify and control any undesirable effect in Quality or Productivity
 
Addition of devices for the removal of polymerization heat
 
Increasing Reactor size has the drawback of reducing heat transfer area of jacket per volume, so the use of chilled water for cooling and the installation of additional heat transfer area are the logical choice.
 
Simultaneously, more active initiator systems, Emulsions and CID (Continuous Initiator Dosing) Technology have been developed to exploit increases in cooling availability and run progressively shorter polymerizations.
JACKET
Primary device that cools directly polymerizing medium by removing sensible heat through reactor wall.
300 - 350 Ton / m3 year (conventional, large reactor)
670 - 720 Ton / m3 year (high efficiency)
Advantages:
o   Minimum impact on suspension stability
o   Operates throughout reaction
Disadvantages:
o   Limited area, dependent on reactor size
o   Built together with reactor, therefore cannot be increased or modified in existing ones 
 
BAFFLES
Device that directly cools polymerization medium by removing sensible heat through baffles surface.
Up to additional 200 Ton / m3 year
Advantages:
o   Higher heat transfer coefficient due to increased turbulence.
o   Operates throughout reaction
o   Can be installed in existing reactors
 
Disadvantages:
o    Higher droplet instability so recipe adjustments are needed to mitigate impacts on Quality
o    Small heat transfer area, limited by reactor size and suspension stability (there is a limit in the number of baffles beyond which proper Quality cannot be attained)
 
REFLUX CONDENSER
Device that condenses vapor of VCM and returns it as liquid to the reactor, removing latent heat of vaporization.
Up to additional 120 Ton / m3 year
Advantages:
o   Highly efficient heat removal
o   Can be installed in existing reactors
 
Disadvantages:
o   Small effective area for condensation
o   Proper sizing (size, length and number of tubes) is essential for trouble-free operation
o   Moderate to strong effect on suspension stability, depending on boiling rate and timing
o   Rate of heat removal limited by excessive boiling that cause foaming, carry-over, clogging, suspension instability and other Quality issues
o   Lower yields due to residence time of a fraction of VCM mass outside polymerization loci
o   Operation limited to certain periods during polymerization
o   Recipe adjustments are needed to mitigate impacts on resin Quality
 
SLURRY HEAT EXCHANGER
Device that cools directly polymerizing medium by removing sensible heat through heat exchanger wall.
More than additional 300 Ton / m3 year
Advantages:
o   Very high overall heat transfer coefficient
o   Can be installed in existing reactors
 
Disadvantages:
o   Not tested yet but technologically feasible
o   Strict methodology to ensure trouble-free operation without negative impact on Quality
 
 
Do you want to troubleshoot the operation of an existing cooling device?
Do you want to increase your Reactor productivity without creating Quality issues?
Do you want a trouble-free increase in your polymerization rate?
Do you want to select or design a new cooling device?
Let me help you understand and safely improve the Productivity
of your reactors to optimize the performance of
your S-PVC resins and Production Plant.
 
View my PROFILE and visit my CONSULTING SERVICES page.

© 2022 Carlos Aguilar / PVC Expertise

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