CO2 Gas Stream Expansion Control to Prevent Solid CO2 Deposition
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Solution Overview
Problem
The formation of solid CO2 in CO2 lean gas streams at low temperatures can lead to clogging and erosion in piping and equipment, posing operational challenges and maintenance issues in power plants, especially during the expansion of CO2 lean gas streams in oxy-combustion power plants.
Innovation Solution
Implementing a low temperature override (LTO) mechanism that allows overriding the pressure controller to increase the pressure of the gas stream when the temperature drops below a predetermined minimum, preventing solid CO2 formation by adjusting the pressure through guide vanes of expanders or bypassing expander components, thereby maintaining stable operation and reducing maintenance requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If the pressure of the CO2 lean gas stream is reduced in an expander to facilitate CO2 removal and reduce flue gas volume, then the dimensions of power plant and gas cleaning arrangements are reduced, but the temperature of the gas stream drops below the predetermined minimum temperature causing solid CO2 formation
Solution Approach 1:
The patent implements a feedback control system where a temperature sensor continuously monitors the temperature of the CO2 lean gas stream downstream of the expander. When the temperature drops below a predetermined minimum threshold, the system automatically activates a bypass line to mix warmer gas back into the stream, preventing solid CO2 formation. This closed-loop feedback mechanism dynamically adjusts the process to maintain temperature within safe operating limits while still achieving pressure reduction for CO2 removal.
Solution Approach 2:
The patent takes preliminary action by providing a bypass line that can introduce warmer gas into the CO2 lean gas stream before solid CO2 formation occurs. The system proactively prevents the temperature from dropping too low by allowing operator intervention or automatic control to bypass the expander undercritical conditions, thereby preventing the harmful effect of solid CO2 deposition before it occurs.
2Productivity
If the temperature of the gas stream is reduced to facilitate CO2 separation, then CO2 removal efficiency is improved, but solid CO2 deposits form causing clogging and erosion in piping and equipment
Solution Approach 1:
The temperature monitoring and bypass control system provides feedback to prevent solid CO2 deposition while maintaining efficient CO2 removal. By continuously monitoring temperature and automatically activating the bypass when temperatures approach the dew point, the system ensures the gas stream remains in a safe temperature range that prevents solidification, thereby protecting equipment from clogging and erosion while still achieving effective CO2 separation.
Solution Approach 2:
The bypass line serves as a protective measure that cushions against the harmful effect of solid CO2 formation. By providing a pre-established alternative path that introduces warmer gas, the system prepares in advance to prevent solidification, thereby protecting the expander, piping, and downstream equipment from the damaging effects of solid CO2 deposits before they can occur.
3Stress or pressure
If a pressure controller is used to maintain predetermined pressure in the gas stream, then pressure control is improved, but the temperature may drop below minimum temperature causing operational issues
Solution Approach 1:
The system employs a dual-parameter feedback control mechanism that monitors both pressure and temperature. The pressure controller maintains predetermined pressure for efficient CO2 removal, while a separate temperature monitoring system with bypass control prevents temperature from dropping below minimum thresholds. This coordinated feedback approach ensures both pressure control and operational reliability are maintained simultaneously.
Solution Approach 2:
The patent introduces dynamic control by allowing the system to switch between normal operation (with pressure control) and bypass mode (with temperature control) based on real-time conditions. The bypass line enables the system to dynamically adjust its operating mode, transitioning from pure pressure control to temperature-controlled operation when solidification risks are detected, thereby maintaining reliability across varying operating conditions.
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 LTO mechanism effectively reduces the formation of solid CO2, facilitating energy recovery and ensuring stable operation by directly addressing temperature changes in real-time, thus minimizing equipment damage and maintenance needs.
Implementation Method 1
the pressure of the CO2 lean gas stream is reduced in an expander
Implementation Method 2
a temperature monitor, such as a temperature sensor or detector that detects the temperature of the gas stream
Implementation Method 3
the pressure of the gas stream section may be raised above the predetermined pressure maintained by the pressure controller when the temperature at that section has become too low
Data Source
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AI summary
The present disclosure relates to a method and an arrangement (1) for expanding a gas stream comprising carbon dioxide, CO2, the method comprising: removing CO2 from a process gas to produce a CO2 lean gas stream comprising residual CO2; monitoring a temperature of the gas stream downstream of an expander (7,10,16); controlling a pressure of the gas stream downstream of the expander by means of a pressure controller (9,15,21); and overriding the pressure controller when the temperature downstream of the expander is below a predefined minimum temperature; whereby deposition of solid CO2 from the residual CO2 in the gas stream is avoided. The disclosure also relates to a gas cleaning system and a power plant, such as an oxy-combustion power plant, associated with the arrangement.