Recirculating Gas Vessel Cooldown for Faster Reactor Turnarounds
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Solution Overview
Problem
Current methods for cooling large process vessels, such as hydrotreaters and catalytic reformers, are inefficient, requiring several days to cool down to ambient temperature, leading to prolonged production outages and high nitrogen costs.
Innovation Solution
A recirculating gas cooling system utilizing a hydrogen-rich gas stream, circulated by an existing recycle gas compressor, is introduced to rapidly cool the vessels through a heat exchanger system, operating at lower pressures and capable of achieving temperatures significantly below ambient.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If traditional cooling methods using ambient air and water-cooled exchangers are used, then the cooling process is simple and requires minimal additional equipment, but the cooldown time extends to several days and the final temperature cannot go below ambient
Solution Approach 1:
The patent introduces a recirculating gas cooling system that circulates process gas through the catalyst bed and cools it via heat exchangers. The recirculating gas acts as an intermediary medium to transfer heat from the catalyst bed to the cooling system, enabling controlled cooldown without direct contact with ambient air or water, thus achieving lower temperatures and faster cooling while managing thermal stress
Solution Approach 2:
The system changes the cooling parameters by controlling gas flow rates, temperatures, and pressures throughout the cooldown process. By adjusting these parameters dynamically, the system optimizes heat removal efficiency while preventing thermal shock to the catalyst and vessel, enabling the vessel to reach temperatures significantly below ambient (e.g., -40°C to -100°C) in a controlled manner
2Loss of time
If nitrogen injection is used to cool the vessel below ambient temperature, then the cooldown speed increases, but the cost of nitrogen consumption becomes excessively high
Solution Approach 1:
The system uses the process gas already present in the vessel and circulating through the catalyst bed as the cooling medium. This self-service approach eliminates the need to import expensive nitrogen, as the recirculating gas is continuously cooled and reused. The system leverages existing process materials rather than consuming additional substances, significantly reducing operational costs while maintaining effective cooling
Solution Approach 2:
Instead of discarding the process gas after use, the system recovers and recirculates it through the cooling exchangers. The cooled gas is then reused for continued cooling, creating a closed-loop system that maximizes the utility of the cooling medium and eliminates the need for continuous nitrogen injection, thereby reducing both time and substance costs
3Productivity
If rapid cooling is attempted to minimize turnaround time, then productivity improves, but thermal stress on the catalyst and vessel increases potentially causing damage
Solution Approach 1:
The cooling system operates dynamically by continuously adjusting gas flow rates, temperatures, and pressure differentials based on real-time conditions in the vessel. This dynamic control allows the system to accelerate cooling when thermal stress is manageable and slow down when approaching critical thresholds, optimizing the balance between productivity and equipment safety throughout the cooldown process
Solution Approach 2:
The system employs periodic cooling cycles with varying intensities, alternating between higher and lower cooling rates. This periodic action prevents sustained high thermal gradients that could cause damage, while still achieving rapid overall cooldown by accumulating cooling effect over multiple cycles, thus protecting the catalyst and vessel while maintaining productivity
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 method significantly reduces the cooldown time, minimizing production downtime and nitrogen costs while ensuring safe catalyst replacement and maintenance access.
Implementation Method 1
A recirculating gas cooling system, which may comprise a heat exchanger system, is introduced into the quench flowline
Implementation Method 2
The recirculating gas cooling system has the capacity to cool a desired flowrate of cooled recirculating fluid, usually gas, at 30 to 40° F. below the ultimate desired process vessel temperature
Data Source
AI summary
A system and method of use of same for cooling process vessels, particularly those having reactor beds inside such as hydrotreaters, hydrocrackers, and catalytic reformers as part of processing units, during unit turnarounds. While the process vessel is in normal operation or in a preliminary cool down phase, quench gas flow is routed through a bypass flow path while a recirculating gas cooling system is installed in the primary flow path, requiring no unit downtime. During a turnaround, the process vessel temperature is lowered to a desired temperature, permitting entry and replacement of catalyst inventory, using the existing hydrogen recirculating (recycle gas) compressor to circulate a recirculating gas stream through the recirculating gas cooling system, the process vessel, and back through the compressor and recirculating gas cooling system. The cooling system removes heat from the circulating flowstream, thus lowering the process vessel temperature, faster than cold nitrogen injection methods.