Absolicon Investigates Wastewater Sludge Drying with 140°C Solar Heat
Municipal sewage sludge is currently used as fertilizer in rural areas in Sweden. However, if a newly proposed law is passed, it will require a two-thirds reduction in this current method of treating sludge.
Due to concerns about contamination from heavy metals and other pollutants, Swedish sewage sludge will need to be dried in the future, which will require heat.
A new solar heating application
This potential new industrial use of solar heat caught the interest of Isak Svensson, a recent civil engineering graduate who, after completing a masters in environmental engineering, was hired by Swedish solar thermal company Absolicon to work on water-related industrial solar thermal applications.
Svensson conducted an initial cost-benefit analysis of sludge drying using concentrated solar energy to supply the hot air at 140°C for drying.
“This is kind of a new application for us,” he said. “We use water in the collectors and we can create steam, but you can also use heat exchangers to get hot air if you want that. It depends on the application, but for the sludge drying that we’re going to look at now, we’re going to use hot air. In my thesis project for Absolicon, which I presented at the SolarPACES conference, I looked at this application for a specific treatment plant and an economic analysis based on several factors such as: B. setting a price for carbon dioxide greenhouse gas emissions, etc.
The project consortium, which includes Huber Waste Water Solutions, a manufacturer of various wastewater treatment applications, will receive $45,000 in funding from the Swedish Innovation Agency to evaluate renewable options for sludge drying – and Swedish participation in Horizon Europe through an application for an EU grant to build a full-scale demonstrator to test the concept.
Next demo level for solar wastewater treatment
“Currently, this project is in the early stages – our next step here is to conduct a more detailed feasibility study,” he said. “We do that with Huber Waste Water Solutions. They have this belt dryer which we believe has promising technical specs for integration with the solar panels so we will do a feasibility study with them and then apply for another grant from Horizon Europe to build a real scale demonstrator, as soon as we have the results of this feasibility study.”
In his master’s thesis, Svensson compared three options to ensure year-round operation: 100% biogas, 50/50 biogas and solar, and 100% solar – with intermediate sludge storage. After calculating three alternatives, he came to the conclusion that a solar-biogas hybrid would be the most economical way to dry wastewater around the clock.
“There have been a lot of developments in thermal storage in Denmark, where you actually dig a really big pit in the ground and store hot water in it,” explained Svensson. “You can make this heat storage so big that you can have a seasonal heat storage; Use it in winter too. You can store the heat for the night, but also for the different seasons.”
The next step is to conduct a more detailed feasibility study to assess the technical integration and optimize the economics, and then to develop a solar sludge drying demonstrator to provide the proof of concept in Sweden, and then to develop this turnkey facility, which Can market production line partners in different parts of the world.
Abolicon operates the largest solar thermal system with concentrating solar energy in Sweden to heat the local district heating network.
They also supply solar systems for industrial customers across Europe such as breweries and chemical producers. Depending on the equipment and the installation space available, the solar panels can be installed on the ground or in a high or roof installation, such as the installation for Colgate Palmolive in Greece. Their turnkey systems for on-site installation include collectors, pumps and control systems.
Learn from PV
One reason for the rapid growth of solar PV is that the technology lends itself to mass production and diverse markets. Individual solar modules are small and scalable. Homeowners can install just a few panels for a roof, and developers can install multiple shipments of panels to build utility-scale solar farms. Online estimation tools are commercially available for end users.
Similarly, the Absolicon website includes an online estimation tool that allows individual industrial heating customers to receive personalized savings estimates for abandoning current heat sources and switching to solar heating.
Absolicon’s field simulator allows potential customers to input the location and size of their potential installation and takes local DNI into account to create estimated costs and results: “Results are shown in real-time and a summary is sent to your email so you can can study the calculations in peace.”
“In our example, we know that drying sewage sludge requires about 0.8 kilowatt hours of thermal energy per kilogram of evaporated water,”
“So if you know how much sludge you have, it’s easy to calculate how much energy it takes to vaporize it. Depending on how dry you want it, you can easily see how big the solar field needs to be.”
A solar panel every six minutes
Absolicon appears to be the first solar thermal collector manufacturer attempting to make the heat-generating form of solar as mass-producible and as easy to order as PV.
The company recently partnered with robotics company ABB to develop an automated assembly line for its parabolic trough solar panels that has cut manufacturing time from three units a day to one every six minutes. The aim is to have production line partners in every country who can produce the collectors for such applications.
Absolicon estimates that by producing a solar panel every six minutes with ABB’s robotics, they can make their solar trough panels cost-competitive with fossil fuel energy for industrial heat. So Absolicon would be well positioned to become a global supplier of mass-produced solar collectors for these and many other industrial heating applications.