High-Quality Biomass Material Drying Using 400 kW of CW RF Power

Schaumburg, Illinois, December 21, 2020.


In 2019 Crescend Technologies was commissioned to design, develop and deploy at a customer site, a 200Kw System to be used for large scale biomass drying.  The foundation of this system includes eight (8) Crescend PTL-50 Solid State Microwave Generators covering the 902-928 MHz band.

Crescend’s PTL-50 (figures 1 and 2) has 80dB of system gain, twenty-two 2.5kW CW RF power modules (SSPA-Blades) combined with a 22-1 radial combiner with 7-16 DIN inputs and WR975 waveguide output, 55% AC-to-RF efficiency at full power output, gain and phase control, water cooling with primary and secondary manifolds and tubing, 480 VAC distribution panel and a system control distributed high-speed multi-processor architecture.  Eight of these generators were successfully commissioned to produce 400 kW of CW RF power into a given applicator to dry high-quality biomass material.  The project from concept to design and manufacture, at Crescend’s facility, was achieved in less than 9 months.

50Kw Generator Side
Crescend PTL-50 50 kW High Power Solid State Microwave Generator

Figure 1: Internal view of Crescend PTL-50, 50kW Generator/Amplifier


PTL 2.5 SSPA-Blade solid state amplifier inside PTL-50 50 kW Microwave GeneratorMicrowave Color
PTL 2.5 SSPA-Blade solid state amplifier inside PTL-50 50 kW Microwave Generator

Figure 2: Internal View 50kW Generator with Liquid Cooled SSPA-Blades (Crescend PTL-50)


Scope of Work:

Scope of work included design, construction, test, delivery and commission of eight (8) 50 kW solid-state RF generators to a customer site to be used for drying hemp as shown below in figure 3.

Figure 3: Eight (8) 50 kW generators (Crescend PTL-50) combined two each with a “magic tee” installed at customer site in 2019

The large-scale drying plant is located in a remote location in Arizona where thousands of acres of hemp are cultivated for CBD oil production. The plant is equipped with a 400 cubic foot mixer/dryer with a processing capacity of about 24 tons per day of fresh hemp. The plant is pre-configured for installation of two additional dryers in the future. After drying, the hemp is pelletized and packed in bulk bags, which are then transported to an extraction facility. See figure 4.

Large Scale Bio Mass Drying
Biomass drying using large scale solid state microwave generators

Figure 4

Bio Mass RF Drying
Industrial Microwave Biomass Drying

   Figure 5

The mixer dryer is installed on a steel mezzanine for easy access and to allow bottom discharge of dried product to a conveyor system as shown in figure 5.

A top view of the mixer/dryer, showing the loading port, exhaust duct, and waveguide which delivers microwave power from the generators shown in figure 6.

Biomass Industrial mixer
Microwave drying mixer

Figure 6 Customer drying tank/applicator with four 100 kW inputs

Crescend PTL-50, 50 kW Solid State Microwave Generator installed
Crescend PTL-50, 50 kW Solid State Microwave Generator installed

Figure 7:  Eight (8) Crescend PTL-50 high power solid state RF generators installed

This system is powered by eight Crescend Technologies 50 kW solid state microwave generators. Two 50 kW generators were combined with a “magic tee” to produce 100 kW. These units have extremely high reliability and minimal maintenance, which is especially important at this remote site. See figure 7.

Crescend PTL-50's combined
Combining of PTL-50 Microwave Generators

Figure 8: Shows the combining of eight (8) Crescend PTL-50 high power solid state RF generators.

Dates of Performance:


Start of project March 31, 2019.  Dates of performance October 14, 2019 for the prototype demonstrator through January 15 2020 for commissioning on customer site.


Performance Records:


Per the customer specification, the project was gauged on reducing high quality biomass hemp with a starting moisture level of hemp at 50% to be dried to 10% over set period of time with a 400 kW of power at 902-928 MHz to a given applicator.

The moisture content of the hemp can vary considerably depending on the variety, location, climate, and even the time of day it is harvested. A reasonable average value for estimating is 75%. The density of the hemp determines how much material can be loaded into a given sized mixer/dryer. It is affected by the nature of the hemp (flower/bud/leaf proportion) and how it is cut and chopped. The weight of the hemp itself causes compression which increases loaded density with larger mixer/dryers.

Example Process Rates and Times

For a given amount of hemp, the drying time will depend on the amount of microwave power available and the moisture content of the hemp. A 2 hour cycle time is generally is a good balance between drying speed, moderate drying temperature, and equipment cost. The tables below illustrate performance of various size mixer/dryers configured with sufficient microwave power for 2 and 3 hour drying cycle times. These examples assume flowers and leaves chopped to 10 mm.  See figure 23.


2 hour bio mass drying
2 Hour Biomass Drying using solid state microwave generators

DRYING FROM 75% TO 10% Mixer Capacity (cubic feet) 25, 50, 100, 200, 400


3 Hour process time biomass drying
3 Hour process time using Crescend PTL-50 Solid State Microwave Generators for RF Heating/Drying application



Drying Profiles

Because microwave energy selectively targets water molecules, the temperature of the hemp during drying remains at about 120⁰ F throughout the drying cycle. This is well below the vaporization temperature of essential oils and terpenes, so virtually no loss will occur.

The mixing action of the dryer provides extremely uniform heating without hot spots, so there is no burning or overheating. The hemp retains its natural green color.

The graph below in figure 10 shows the drying cycle of a 200 cubic foot mixer/dryer equipped with 400 kilowatts of microwave power.   The specification of moisture content (MC) of 10% was achieved.

hemp/biomass drying

Figure 10: Drying cycle of a 200 cubic foot mixer/dryer equipped with 400 kW of microwave power.


Significant conversion of CBD-A to CBD occurs during the microwave drying process. The reason this occurs is not well understood, but it is clearly established by laboratory tests. An additional heating step may be added at the end of the drying cycle to ensure 95%+ decarboxylation. This is a software-controlled option.


Crescend has been in business since 1979 and has over 40 years of experience in design, development and manufacture of high-power RF amplifiers.  Our core business has been public safety and military applications.  Safety, quality and reliability is paramount to Crescend.  All products are brought to market with this foundation of rugged, mission critical quality.

Additional previous experience demonstrated in our standard high power, RF amplifiers such as our UHF 250W amplifier, VHF 350W amplifier as well as our PTL 2.5 kW solid state microwave generator.

See Datasheet documents:

Crescend PTL-2.5 Data Sheet for our solid-state microwave generator


Crescend PTL-50 Data Sheet for our 50 kW solid-state high power microwave generator


Crescend P25 Series 900 MHz Data Sheet for our 928-942 MHz 250 Watts Output Power amplifier


Crescend P25 UHF Data Sheet for our low band UHF 250 W amplifier


Crescend P35 Series VHF Data Sheet for our VHF 350 Watts Output Power amplifier


For more information, contact:

Crescend Technologies


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