Biosolids drying can yield Class A products suitable for a wide range of beneficial uses with few restrictions.

But cost-effective drying requires high efficiency and a reliable process that can operate continuously and keep the product pipeline full.

Komline-Wyssmont is now offering its Turbo-Dryer to the municipal wastewater treatment sector. Dryer manufacturer Komline acquired Wyssmont and the Turbo-Dryer in 2022. The technology has been proven for several decades in industrial application for drying hundreds of materials, according to Nathanael Komline, marketing manager with Komline-Sanderson Corp.

The dryer uses direct heat and a stepwise process to deliver uniformly dried biosolids. The material is exposed to heated areas and is intermittently redistributed to speed the drying. Dryer sizes range up to 35 feet in diameter by 60 feet high with an evaporative capacity of 25,000 pounds of water per hour. The units provide continuous automatic operation with precisely controlled temperature and residence time.

The manufacturer says the process creates minimal dust and fines and provides a free-flowing end product that does not cake. The dryers can use a variety of fuels and other heat sources. Komline and Joe Bevacqua, vice president of Komline-Wyssmont, talked about the technology in an interview with Treatment Plant Operator.

TPO: What is the reason for bringing this technology to the wastewater treatment market?

Komline: We have significant experience in biosolids drying. Now we are adding this direct-drying technology to our experience with our existing indirect dryer. Some treatment facilities prefer a direct dryer for their applications. Some dryers that we supplied in the 1950s are still operating in production every day.

TPO: What differentiates this dryer from other biosolids drying technologies?

Bevacqua: We have a very heat-efficient system. We take some of the exhaust gas from the dryer and recirculate it back over the burner or through a heat exchanger to increase the temperature of the incoming ambient air. So for example, in winter we’re taking in fresh air that is very cold, but we preheat that ambient air and therefore use less fuel. The amount of hot air recirculated depends on the amount of water we need to evaporate in the dryer. The units are also relatively compact. Whereas a conveyor dryer or a rotary dryer could be up to 100 feet long, our units are vertical structures. There is a big range of sizes depending on the capacity the customer is looking for.

TPO: What fuels can this dryer use?

Bevacqua: We can use any heat source our customer has available. We can use waste heat, steam, natural gas, oil and biogas. We can handle the material at up to 85% moisture without having to condition the feed.

TPO: How would you quantify the heating efficiency of this technology?

Bevacqua: We can operate with heat requirements as low as 1,650 to 1,800 Btu per pound of water evaporated. For a belt dryer, which is not a sealed unit, the heat requirement is often much higher. In the industrial field, we have seen heat usage as high as 3,300 Btu per pound of water, and that’s for materials with the same water content as municipal biosolids.

TPO: In basic terms, how does the technology work?

Bevacqua: Inside the dryer we have a stack of circular rotating trays, like flat donuts. Down the center of the trays is a shaft with fan wheels mounted on it. Hot air enter the unit is mixed by the action of those fans to control the temperature. Generally for municipal biosolids we are in the range of 250 to 350 degrees F. The hot air circulates over the material on the trays. Wet material enters at the dryer onto the top tray. After one revolution a stationary wiper directs the material through slots down to the tray below, and so on to the bottom of the unit. Every time the material transfers to the next lowest tray, the pile is turned over. That helps dry the material faster.

TPO: How many trays are there?

Bevacqua: That depends on the capacity the customer requires. It can be anywhere from 10 to 48 trays. The dryer can be built with a variety of materials. The trays where the material is flowing would typically be stainless steel. But other pieces such as the walls, the roof and the support structure can be stainless, or plain steel, in which case there is probably a 25% reduction in price.

TPO: Is each dryer custom designed for the site?

Komline: As with most of our equipment, they are engineered to order. That’s partly where the experience of Komline comes in.

Bevacqua: We size the equipment based on test data. On each project, we calculate the amount of heat necessary and size all the auxiliary equipment like fans, burner, dust collector and scrubber if necessary. Then we run tests on a sample of the customer’s material. We have a bench-scale unit that duplicates all the actions of a full-scale production unit. From a test using about two pounds of material, we can scale up to any capacity and guarantee performance.

TPO: What is the capacity range of the dryers?

Bevacqua: If you have a product that’s 80% wet and 20% solids, our biggest units can evaporate about 12,000 pounds of water per hour. That yields about 3,000 pounds of solids. Units from 4 to 12 feet diameter and about 17 feet tall are shipped shop-assembled. Units larger than that are field-assembled from subassemblies.

TPO: How easy is it to operate the technology?

Bevacqua: It operates automatically with essentially no operator attention. Customers have told us they turn it on Monday morning and nobody watches it. It runs continuously. No plant assigns an operator to watch the Turbo-Dryer.

TPO: What does regular maintenance consist of?

Bevacqua: Generally, maintenance is less than 1% of the cost per year. The bearings are designed for a 20-year life because the rotational speeds in the dryer are quite low. The only wear items are the wiper blades, which are made from tempered 316 stainless steel. Because the material being dried is continuously wiped from the trays, the system requires minimal cleaning.