Heat Pump Compressor Segmentation for Hydrocarbon Separation
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Solution Overview
Problem
Current hydrocarbon separation processes, such as propylene-propane splitters, are energy-intensive due to low relative volatility, requiring large distillation towers and significant refrigeration systems, leading to inefficiencies in heat recovery and increased utility consumption.
Innovation Solution
Implementing a system with a single-stage heat pump compressor and a multi-stage heat recovery compressor, where liquid from the heat recovery compressor's second stage suction drum is used to condense the deethanizer and pump out propylene liquid product, and the vapor from the PP Splitter column overhead is processed in a centrifugal heat pump compressor, with separate machines for better control and flexibility, allowing for more efficient heat recovery and reduced utility needs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-stage heat pump compressor is used to condense the deethanizer overhead, then capital costs and device complexity are reduced, but control flexibility and adaptability deteriorate
Solution Approach 1:
The compressor system is segmented into two independent units: a first heat pump compressor dedicated to the deethanizer overhead condensation and a second heat pump compressor for the PP splitter overhead condensation. This segmentation allows each compressor to be independently controlled and optimized for its specific duty, maintaining adaptability while reducing the complexity of any single unit.
Solution Approach 2:
The second heat pump compressor serves multiple functions: it condenses the PP splitter overhead vapor and also provides refrigeration for the deethanizer by receiving vapor from the deethanizer overhead after it has been compressed by the first compressor. This multi-functionality allows a single compressor to handle multiple duties, improving versatility without significantly increasing overall system complexity.
2Use of energy by moving object
If heat is recovered from deethanizer overhead and transferred to depropanizer, then energy efficiency improves and LP steam consumption is reduced, but system complexity increases
Solution Approach 1:
The heat recovery function is merged with the existing heat pump compression system. The second heat pump compressor's discharge vapor, which would normally be condensed by a separate refrigeration system, is instead routed to serve as the heating medium for the depropanizer reboiler. This merging eliminates the need for separate heat recovery equipment and integrates multiple functions into the existing compressor system.
Solution Approach 2:
The waste heat from the compressor discharge vapor, which would normally be rejected to cooling water or air, is converted into a useful heating resource for the depropanizer reboiler. This converts what would be a harmful waste product into a beneficial energy source, improving overall energy efficiency while utilizing existing system components.
3Loss of energy
If a multi-stage heat compressor system with three stages is used, then heat recovery capability improves, but device complexity and utility requirements increase
Solution Approach 1:
The two-stage compression system maintains continuous useful action by ensuring that the discharge vapor from each stage is immediately utilized. The first stage discharge vapor is used for deethanizer condensation, and the second stage discharge vapor is used for depropanizer heating. This continuous utilization of compression work eliminates energy losses and maintains high heat recovery capability without requiring additional complex equipment.
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 configuration enhances energy efficiency by recovering heat from the deethanizer overhead and transferring it to the depropanizer, reducing LP steam consumption and capital costs, while maintaining independent control of column duties.
Implementation Method 1
the overhead vapor of the PP Splitter is compressed to the required pressure, typically between 1,034 to 1,724 kPag (150 to 250 psig), which is the minimum temperature for a heat exchanger to condense vapor on the hot side and re-boil liquid on the cold side
Implementation Method 2
which is the minimum temperature for a heat exchanger to condense vapor on the hot side and re-boil liquid on the cold side of the heat exchanger
Implementation Method 3
this stream is flashed across a valve into a suction drum down to the column overhead pressure to provide Joule-Thomson effect cooling to the column overhead
Data Source
Figure 1
Figure 2
AI summary
Systems and processes for heat recovery associated with the separation of hydrocarbon components. Two compressors are used to compress a portion of an overhead vapor stream from a fractionation column. A pressure of the liquid portion of the compressed overhead is reduced and used to recover heat from an overhead of another separation zone having a fractionation column. Once the heat has been recovered the stream is recompressed. The recovered heat may be removed from the recompressed stream in a reboiler of another fractionation column. The fractionation columns may comprise a deethanizer stripper, propane-propylene splitter, and a depropanizer column.