What is Microwave Pyrolysis?

Microwave Pyrolysis is a method of thermal decomposition that utilizes microwave radiation to break down organic materials into smaller molecules in the absence of oxygen. This process involves exposing the material to high-frequency microwaves, which generate internal heat through the selective absorption of energy by the organic compounds. As a result, the material undergoes pyrolysis, producing volatile gases, liquids, and char. This technique is used to treat various organic waste streams, such as biomass or certain types of industrial waste, with the aim of converting them into products like bio-oil, syngas, or biochar. 

Microwave pyrolysis offers advantages such as rapid heating, precise control over reaction conditions, and potentially higher product yields compared to conventional pyrolysis methods (for instance slow pyrolysis, fast pyrolysis, flash pyrolysis). Microwave pyrolysis can be broadly categorized based on the type of microwave-generating devices used. The two main categories are processes using magnetrons and processes using solid-state devices. 

Magnetron-Based Microwave Pyrolysis 

Traditional microwave pyrolysis systems utilize magnetrons, which are vacuum tube devices that generate microwave radiation. In these systems, the magnetron emits microwaves at a specific frequency, typically 2.45 GHz, which are then directed into the reaction chamber to heat the material and induce pyrolysis. This method is well-established, cost-effective, and widely used in both laboratory and industrial settings. 

Solid-State Microwave Pyrolysis 

In contrast to magnetrons, solid-state microwave generators use semiconductor-based components, such as transistors and diodes, to generate microwave radiation. Solid-state devices provide greater flexibility compared to magnetrons in controlling the frequency and power levels of the microwaves. This flexibility enables better tuning of the microwave energy to the specific requirements of the pyrolysis process. 

Drawbacks of the Magnetron-Based Microwave Pyrolysis 

While magnetron-based systems are well-established and cost-effective, solid-state microwave systems offer more flexibility in terms of frequency control and modulation, potentially allowing for better optimization of the pyrolysis process. 

In the magnetron-based pyrolysis method, some of the challenges faced by the users include: 

- Inconsistent and non-uniform heating patterns: Magnetron-based pyrolysis can lead to inconsistent and non-uniform heating patterns within the material being processed. This is primarily due to the nature of electromagnetic waves emitted by the magnetron, resulting in uneven distribution of energy within the reaction chamber. Variations in material composition, size, and positioning can contribute to localized hotspots and temperature gradients, impacting the overall uniformity of the pyrolysis process. 

- Short Mean Time Between Failure (MTBF): Magnetron-based pyrolysis systems can experience a relatively short mean time between failure (MTBF). The continuous operation and high-power levels associated with magnetrons may lead to wear and degradation of these vacuum tube devices over time, affecting their reliability. Frequent maintenance and replacement of magnetrons may be required in industrial applications to ensure consistent performance and prevent unexpected downtime. This frequent need for replacement not only increases the cost of operation but also negates the low initial procurement expenses of magnetrons.

What are the Benefits of Using Solid-State Devices Compared to Magnetrons?

Solid-state microwave pyrolysis addresses these issues associated with magnetron-based microwave pyrolysis. Enhanced control and modulation capabilities of solid-state devices enable more precise tuning of microwave frequency and power levels. The frequency agility of solid-state devices can also assist in enabling better adaptation to the specific characteristics of the material being processed. 

Solid-state devices generally have higher efficiency and reliability which contributes to improved energy conversion and utilization during pyrolysis. Moreover, the longer lifespan and lower susceptibility to wear and degradation in solid-state devices result in extended mean times between failures. This characteristic reduces the frequency of maintenance and replacement, enhancing the overall reliability and longevity of the microwave pyrolysis system. 

RFHIC Case Study

In a similar scenario, RFHIC partnered with Scanship to replace magnetrons with a GaN solid-state microwave generator to design a stable microwave pyrolysis system that efficiently converts carbon-based ship waste into valuable biofuels. RFHIC is a global leader in designing and manufacturing GaN-based RF/Microwave devices and high-power generator systems for various applications. Scanship is a Norwegian company that develops microwave pyrolysis systems for waste gasification that are installed on commercial cruise ships. These systems collect and convert the biowaste generated onboard into valuable biofuels such as hydrogen and biochar. 

Heat distribution model using RFHIC's GaN microwave generator.RFHIC introduced the RIK0930K-40TG GaN solid-state microwave generator as an alternative to magnetrons. The RIK0930K-40TG is a 30 kW microwave generator that operates from 900 – 930 MHz and is fabricated using RFHIC’s cutting-edge gallium-nitride (GaN) on silicon-carbide (SiC) technology. This solid-state microwave generator comes fully equipped with a 3-phase 380V AC power supply unit, a control module, and eight solid-state power amplifier shelves. 

Unlike magnetrons, RFHIC’s RIK0930K-40TG provides precise digital controllability of both frequency and phase. This capability allowed Scanship to tailor the pyrolysis system's operating conditions based on the organic waste composition, resulting in more uniform and consistent heating patterns for processing increased waste volumes efficiently.

GaN Solid-State Microwave Generators vs Magnetrons 

Additionally, operating at lower voltages (50 V) and boasting lifetimes of up to 100,000 hours, the RIK0930K-40TG incorporates eight power amplifier shelves with redundancy. In case of malfunctions in one or two shelves, the generator continues proper operation until replacements are installed. RFHIC's GaN solid-state microwave generator significantly improved the yield of hydrogen and biochar, outperforming magnetrons in terms of lifespan and stability. The built-in redundancy feature not only enhances system reliability but also reduces the frequency of unit replacements, lowering maintenance and operational costs for Scanship. 

Hence, RFHIC helped Scanship in enhancing the quality, efficiency, and reliability of microwave pyrolysis through the implementation of GaN microwave generators. This collaboration improved the overall performance of Scanship's waste processing system and highlighted the potential of GaN solid-state microwave generators as an alternative to traditional magnetrons, offering a more sustainable and effective solution for organic waste treatment.

Click here to learn more about the RIK0930-40TG Microwave Generator.