Application Analysis of Tubular Heaters in Propane Dehydrogenation Units
1. Overview of Propane Dehydrogenation Technology
Propane dehydrogenation (PDH) technology is an important process for the production of propylene. With the increasing demand for propylene, PDH units have been widely applied in recent years. Currently, the main PDH technologies include UOP's Oleflex technology, Lummus' Catofin technology, ThyssenKrupp's STAR process, Linde/BASF's PDH process, and Sinopec's SPDH technology.
2. Application of Tubular Heaters in Propane Dehydrogenation Units
Tubular heaters are key equipment in propane dehydrogenation units, primarily used to heat reaction feedstocks to the high temperatures required for the reaction. Below are the application characteristics of tubular heaters in several major PDH technologies:
2.1 UOP's Oleflex Technology
The Oleflex process uses a moving-bed technology with reaction temperatures of 600–630°C and pressures greater than 0.1 MPa. The tubular heater in this process is mainly responsible for heating the mixture of fresh propane and recycled propane to the reaction temperature before it enters the reactor for dehydrogenation.
2.2 Lummus' Catofin Process
The Catofin process employs a circulating multi-reactor system. The tubular heater heats the mixed propane to the reaction temperature before sending it to the reactor. A notable feature of this process is the use of high-heat-capacity materials (HGM) in the reactor to increase heat storage and reduce energy consumption.
2.3 ThyssenKrupp's STAR Process
The STAR process uses a fixed-bed tubular reactor with reaction temperatures of 500–580°C. Its tubular heater consists of a top-fired tubular reactor connected in series with an adiabatic oxidation reactor. The reactor is packed with 80% catalyst, while the oxidation reactor contains 20%.
2.4 Linde/BASF's PDH Process
This process uses a multi-tube fixed-bed reactor. The tubular heater is a top-fired conversion furnace with reaction tubes packed with catalyst. The reaction occurs under nearly isothermal conditions, which helps reduce propane cracking and coke formation.
2.5 Sinopec's SPDH Technology
The SPDH process employs a moving-bed reactor. The tubular heater has a box-type structure with multi-pass U-shaped low-pressure-drop tubes and low-NOx burners. The heater's design thermal efficiency can reach 95%, and it is equipped with a waste heat recovery system to preheat combustion air.
3. Design Considerations for Tubular Heaters
The design of tubular heaters in propane dehydrogenation units must consider the following key points:
Heat Intensity and Mass Flow Rate: Precise control of heat intensity and mass flow rate is required to ensure heating efficiency and reaction conditions.
Preventing Flow Maldistribution: The design should avoid maldistribution within the tubes to ensure uniform heating.
Minimizing Thermal Cracking: Optimizing tube structure and operating conditions helps reduce propane cracking and coke formation.
Pipeline Stress Analysis: Given the high temperatures and significant thermal displacement of the heater's piping system, stress analysis is crucial. Optimizing pipeline layout and support design can prevent weld cracks and flange leaks.
4. Optimization and Improvement Measures
To enhance the performance and reliability of tubular heaters, the following optimization measures are widely applied:
Advanced Tube Structures: Using multi-pass U-shaped low-pressure-drop tubes reduces pressure drop and energy consumption.
Waste Heat Recovery Systems: Installing steam generators and air preheaters improves energy efficiency.
Low-NOx Burners: Employing low-NOx burners reduces pollutant emissions.
Stress Analysis and Optimization: Detailed stress analysis helps optimize the piping system design to avoid equipment failures caused by thermal stress.
5. Conclusion
Tubular heaters play a vital role in propane dehydrogenation units, and their design and optimization directly affect the efficiency and reliability of the unit. By selecting appropriate process technologies, optimizing design parameters, and applying advanced equipment and materials, the performance of tubular heaters can be significantly improved. This leads to reduced energy consumption and enhanced overall unit efficiency.
