Hydrocarbon Heat Pump Compressor Decoupling
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Solution Overview
Problem
The existing hydrocarbon separation processes, such as propylene-propane splitters, require high energy due to low relative volatility of propylene and propane, leading to inefficient heat recovery and increased utility requirements in traditional heat pump designs.
Innovation Solution
A process that decouples the first and second stages of the heat pump compressor, allowing the first stage to process only column overhead vapor and the second stage to handle excess condensing energy, with heat transfer between stages to optimize heat recovery, and includes a second separation zone with higher pressure to manage vapor and liquid streams efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a traditional two-stage heat pump compressor is used where the second stage discharge is flashed back to column overhead pressure, then the vapor from the flash is re-processed in the heat pump stages, but this increases the overall capacity and utility requirement of the compressor
Solution Approach 1:
The patent extracts the flash vapor stream from the re-processing cycle by directing it directly to the column overhead instead of routing it back through the heat pump compressor stages. This eliminates the unnecessary compression and heat exchange steps for this stream, reducing compressor capacity requirements while maintaining heat recovery from the condensed liquid portion.
Solution Approach 2:
The patent segments the handling of the second stage discharge stream by separating the liquid and vapor phases after flashing. The liquid portion undergoes heat recovery and condensation, while the vapor portion is directly returned to the column overhead. This segmentation allows each phase to be processed optimally without the inefficiency of re-compressing the vapor.
2Manufacturing precision
If a very large distillation tower with 150 to 250 trays is used to separate propylene and propane, then the separation is achieved, but the energy required for separation becomes very high
Solution Approach 1:
The patent changes the pressure parameter in the second separation zone to a higher pressure than the overhead stream pressure. This pressure change enables more efficient heat transfer and condensation processes, allowing the system to achieve the required separation purity with reduced energy input compared to conventional atmospheric or low-pressure operation.
Solution Approach 2:
The patent merges the heat pump compression function with the separation process by using the compressed and condensed streams directly in the separation zones. The heat exchangers serve dual purposes of heat recovery and product condensation, integrating multiple functions into fewer units and reducing overall energy requirements.
3Loss of energy
If heat is removed from the column overhead for condensing and transferred to the tower bottoms for re-boiling, then the heat recovery is achieved, but extra vapor from the first stage discharge requires additional heat removal capacity
Solution Approach 1:
The patent introduces a second separation zone operating at higher pressure as an intermediary between the heat pump compressor and the column overhead. This intermediate zone allows for efficient condensation of the compressed vapor and provides a pressure-matched interface for heat transfer, eliminating the need for oversized heat exchangers to handle excess vapor capacity.
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 process reduces compressor size and utility needs, eliminates the need for a reflux pump, and achieves significant capital and utility savings while enhancing heat recovery efficiency in hydrocarbon separation.
Implementation Method 1
passing at least a portion of the overhead stream to a compression zone, the compression zone configured to produce a first output stream and a second output stream
Implementation Method 2
transferring heat from at least a portion of the first output stream of the compression zone to the first separation zone
Implementation Method 3
removing heat from the second output stream of the compression zone
Implementation Method 4
passing the second output stream of the compression zone to a second separation zone, wherein the second separation zone has a pressure higher than a pressure of the overhead stream
Data Source
AI summary
A process for recovering heat from the separation of hydrocarbons. The overhead vapor stream from a fractionation column is passed to a two stage heat pump compressor. The first stage of compression is used to reboil the fractionation column. The second stage is compressed and cooled passed to a separation zone. The liquid in the separation zone may be passed back to the fractionation column as secondary reflux, and/or recovered as liquid product. Heat may also be removed from the second stage. A suction drum on the first stage may be used to protect the heat pump compressor from any droplets in the overhead stream.