Reactor Wall Heating via External Heat Tracing
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Solution Overview
Problem
Reactor vessels used in hydroprocessing at elevated temperatures and pressures face significant downtime due to slow heating processes, which increase the risk of structural failure and reduce productivity, as conventional methods require limiting pressure until the ductile-to-brittle transition temperature is exceeded.
Innovation Solution
The method involves using heat tracing to rapidly heat the external walls of the reactor to achieve the minimum pressurization temperature within 5 hours or less, allowing for increased pressure and further heating with internal gas flows to reach operating conditions efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional heating methods are used with pressure limited to 250 psig or less, then reactor wall strength is maintained above the ductile-to-brittle transition temperature, but startup time increases to 24 hours or more
Solution Approach 1:
The reactor wall is pre-heated to the minimum pressurization temperature (95°C or more) using external heating means (steam tracing, electric heating, or hot gas circulation) before introducing the heated gas flow. This preliminary heating action ensures the reactor wall has sufficient strength to contain high pressure before the main heating process begins, reducing startup time from 24+ hours to 5 hours or less.
Solution Approach 2:
The heating process is divided into distinct phases: (1) initial heating of reactor wall to minimum pressurization temperature using external heating means while maintaining low pressure, (2) introduction of heated gas flow for main heating to operating temperature, and (3) pressure increase to operating pressure. This segmentation allows each phase to be optimized independently, achieving both safety and speed.
2Productivity
If pressure is increased before reaching minimum pressurization temperature, then productivity improves through faster startup, but reactor wall strength becomes insufficient leading to potential structural failure
Solution Approach 1:
The reactor wall temperature is raised to the minimum pressurization temperature (95°C or more) using external heating means before any pressure increase occurs. This preliminary thermal conditioning ensures the reactor wall has adequate strength to contain the subsequent high-pressure operation, enabling rapid startup without compromising safety.
Solution Approach 2:
The conventional approach of using internal gas pressure for heating is replaced with external heating means (steam tracing, electric heating elements, or hot gas circulation systems) for the initial heating phase. This substitution allows independent control of temperature and pressure, enabling the reactor wall to be heated to sufficient temperature before pressure is applied.
3Loss of energy
If heated gas flow is used for heating at low pressure, then heating efficiency is reduced due to large mass of reactor walls, but structural safety is maintained
Solution Approach 1:
External heating means are applied to the reactor wall before introducing heated gas flow, creating a thermal pathway that reduces the overall heating time. The external heating pre-conditiones the reactor wall, making subsequent heating by gas flow more efficient and reducing energy loss.
Solution Approach 2:
External heating means act as an intermediary system that transfers thermal energy to the reactor wall more efficiently than direct gas flow heating. This intermediary heating mechanism overcomes the limitation of heating large mass reactor walls at low pressure, while the staged approach maintains structural safety.
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 approach significantly reduces startup time from 24 hours to 2-5 hours, minimizing downtime and increasing productivity by allowing for faster achievement of operating temperatures and pressures while maintaining safety by avoiding excessive pressure until the reactor is adequately heated.
Implementation Method 1
heating an external wall surface of the reactor wall using heat tracing
Implementation Method 2
passing a pressurizing gas flow into the reactor to increase the pressure in the reactor by 0.5 MPa or more and/or to increase the pressure in the reactor to 2.0 MPa-g or more
Implementation Method 3
passing a heated gas flow into the reactor to increase the temperature of the reactor wall by 50° C. or more relative to the first temperature and/or to increase the temperature of the reactor wall to 200° C. or more
Data Source
AI summary
Systems and methods are provided for performing the initial heating phase for a thick wall reactor, such as a hydroprocessing reactor, by using heat tracing to heat the exterior walls of the reactor. Instead of attempting to initially heat the reactor by passing a low pressure heat transfer gas through the interior of the reactor, external heater(s) placed under the reactor insulation can be used to heat the exterior of the reactor. An example of a suitable external heater is a heat tracing blanket, where heat is provided by passing steam through pipes in contact with the external surface or by electrical heaters in contact with the external surface. This can allow for more rapid heating of the reactor, so that a target temperature can be achieved in a time of 5.0 hours or less.