CASE STUDIES

CENTRAL HIGHLANDS, SCOTLAND

AMW IBERS and Carbon Gold impress in DECC Wetland Biomass to Bioenergy Competition

The UK undertakes a considerable amount of land management activities on private and public land, maintaining parkland and conserving wildlife habitats such as natural wetlands. This land management results in the production of surplus biomass that in many cases is either burned or left to decompose, which releases carbon dioxide emissions into the atmosphere, or is disposed of at cost. Last year DECC invested £2m in projects to develop and demonstrate efficient bioenergy systems that optimise existing wetland management activities and add value to the resulting biomass.

Project Kade, a working partnership between AMW and the Institute of Biological, Environmental and Rural Sciences (IBERS) and overseen by Jonathan Walker, will see one such scheme revolutionise wetland management at Cairngorms National Park in Scotland. Located at the RSPB’s reserve, Insh Marshes, which is one of the few ‘natural’ floodplains left in the UK, the area is of national importance for breeding wader birds where balanced management of vegetation is essential to species survival. Grazing wetlands is key however, coarse vegetation such as soft rush, deschampsia and willow scrub is unpalatable to livestock. This can lead to a build-up of dense undergrazed tussocky vegetation across large areas of the wetland. The dense vegetation discourages the waders from feeding and nesting, they need access to the soils to probe for insects and require an open landscape where they see potential predators. Consequently, the increase of invasive vegetation has been linked to the 40% decline in breeding farmland waders and a 60% decline in lapwings between 2000 and 2010.

The work undertaken by Project Kade will provide a unique, energy positive environmental management system that helps return the natural balance of the wetlands. In this impressive closed-loop process, invasive rushes, reeds and willow will be harvested and turned into biochar-based briquettes, their removal allowing grasses to flourish and bird species to thrive.

Invasive rush is harvested using a Softrak harvester, especially designed to cope with tussocky, multispecies swards. The harvester can traverse sensitive areas without causing compaction of the ground and gathers the cut rushes which are taken away for baling and wet storage. The harvested biomass is processed through a screw-press to create a fibrous ‘press cake’, which is later dried. The screw-pressing process also generates a press fluid, which is used to supply an anaerobic digestion unit to produce biogas – which in turn delivers the thermal and electrical energy required to power the process (allowing the process to run completely ‘off grid’). Any digestate by-product produced will be used as fertilizer on local farm land.

Insh marshes, Invertromie Meadow - Softrak fitted with a front mounted forage harvester (cut & collect system) harvesting biomass

Insh marshes, Invertromie Meadow – Softrak fitted with a front mounted forage harvester (cut & collect system) harvesting biomass

 

Invasive reed is harvested and processed into biochar using the pioneering SuperChar 500 kiln from Carbon Gold, with the resulting heat contributing to the press cake drying. Small, invasive trees such as willow are chipped and used as fuel for the kiln. The dried rush press cake and the reed biochar is then homogenised and fed into a briquetter to produce solid fuel briquettes, which will be sold in shops within a 35 mile radius of the processing plant.

The SuperChar 500 kiln is designed to provide a flexible solution for four specific roles in this project

• Drying wet press cake to the moisture level required for fuel briquetting
• Field processing reed to char to improve the fuel value of the briquettes and minimise transportation costs
• Converting drier late harvest rush to char
• Providing a heat source for additional drying capacity, using the available wood chip (dried if necessary) as the energy source

superchar-500

This unique project fulfils DECC Wetland Biomass to Bioenergy Competition objectives to design, develop and demonstrate an efficient, end to end bio-energy system that utilises biomass arising from wetland management activities in that it offers:

• Optimisation of wetland harvesting activities in challenging UK wetland areas and in a manner sympathetic to conservation requirements
• Efficient production of bioenergy feed stock utilising the resultant biomass (reeds, rushes, grasses and sedges) that comply with emission standards or equivalents when used to generate energy
• A cost effective and energy/carbon efficient bioenergy conversion process capable of utilising the specified surplus biomass

DECC says that managing and processing waste in this way will be an ‘important culture shift in progressing the future use of these new feedstock in the bioenergy chain’, one that ‘needs to be made by the conservationists and other land managers that have previously considered this material problematic’. Carbon Gold is excited to deliver a key part of this efficient, carbon positive waste management process that will allow the wetlands and their inhabitants to thrive once again.