Evaporation project manages manure

Livestock waste management is a problem facing the global farming industry. Although manure has the potential to harm the environment and contribute to climate change, manures and slurries represent a valuable resource that can return valuable crop nutrients to farmland. Cost-effective and integrated solutions are needed to address the problem.

Up to 90% of pig and cattle slurry is water, meaning that water content reduction is an effective way to reduce overall volume. As well as reducing storage requirements, the method can reduce potential odours and gaseous emissions during application.

A European project coordinated by HRS Heat Exchangers Sales and Product Development Director Arnold Kleijn looked at how to improve practices for pig producers in Spain, many of whom were reliant on off-site treatment plants to reduce slurry and manure volumes. With transport costs accounting for 60% of the total processing cost, a better alternative was sought.

The project, completed in 2013, cut treatment costs by 40%, sped up the treatment process, reduced energy consumption by 25%, cut slurry volumes by 60% and created potential revenue streams for farmers via nutrients and biogas.

Another aim of the project was to devise a small-scale solution for use on farms. The HRS Heat Exchangers engineering team, using their experience with evaporation and concentration systems, devised a system for direct use on manures and slurries or, in the case of on-farm biogas plants, on the digestate which remains after the anaerobic digestion process.

Arnold Kleijn explained, “The thermal energy needed for evaporation can often be obtained from nearby combined heat and power plants at little or no cost. One of the keys to success was improving the scraping action in the evaporator and preventing the concentrated manure from sticking to the surfaces. This increased heat transfer rates two- to threefold, increasing efficiency and speeding up the evaporation process. By combining the various technologies, we reduced slurry volume by up to 60%, resulting in less storage requirements and fewer tanker journeys.”

As part of the EfficientHeat consortium, HRS Heat Exchangers has continued to develop technology to improve the efficiency of the evaporative system and make it a practical solution for use on farms. Unicus Series scraped-surface heat exchanger technology is used for evaporation and acid dosing reduces volatile ammonia in the process. This strategy reduces odours and creates ammonium sulfate, which is useful as a crop fertiliser.

Image credit: ©Simone van den Berg/Dollar Photo Club