A commitment to 20 per cent use of renewable gas by 2030 - a target that Gas Networks Ireland supports - throws up an opportunity for gas-competent engineering and agri-sector. [caption id="attachment_40580" align="alignright" width="300"] Illustration of the on-farm renewable gas system[/caption] A figure greater than 90 per cent of this is projected to be from biogas resources and is the main focus of this article, but other renewable gas developments include synthetic gas and green hydrogen (referred to as power-to-gas), both of which are in earlier stages of development.

Generated through process of anaerobic digestion

Renewable gas is generated principally through a process called anaerobic digestion (AD). In order to make the gas, feedstocks such as animal slurry, agri-residues, break/catch crops, grass silage, and food industry wastes are heated and agitated in an oxygen-free environment to produce biogas, bio-fertiliser and CO2. The process eliminates a wide range of emissions that would otherwise be going to atmosphere (methane, CO2, H2S) and has three primary outputs and is illustrated above: • The biogas is purified to create bio-methane, and is identical to natural gas. This displaces natural gas supply with a carbon neutral gas; • The bio-fertiliser retains all of the nutrients from the feedstock and is fully absorbed in land spreading. This eliminates the GHG emissions from current land spreading practices where only 10 per cent to 20 per cent of nutrients are absorbed and also displaces imported fossil based artificial fertiliser. Air and water quality are also significantly improved in this process, as well as the land productivity; • The CO2 can be processed to different grades for use in industry or horticulture, displacing emissions from fossil energy produced CO2. To achieve the 2030 target, GNI envisages 400 farm-based ADs and 50 larger ADs configured for co-digesting food industry wastes. Biogas processing would take place on site at each AD facility or in group schemes, where the gas is purified and stored on ADR certified trailer units for collection and delivery to gas entry hubs on the gas network.

Gas network hubs will facilitate AD development in large catchment areas

An example of these trailer units is shown in the main picture. These gas network hubs will facilitate AD development in large catchment areas and GNI aims to commission one facility every nine months, with the first facility due for commissioning in April this year in Co Kildare. This first project is co-funded by the EU connecting Europe facility, GNI and Green Generation, and is part of the Causeway Project, which also includes 14 publicly accessible CNG filling stations. The first AD facility feeding this site will be Green Generation’s existing unit in Nurney, Co Kildare. GNI and Green Generation are engaged with several other AD developers in the catchment area to utilise the hub facility which has a capacity to supply two per cent of the residential heat market or 600 CNG buses. [caption id="attachment_40581" align="alignright" width="300"] Hectare grass to gas delivers energy for nine houses versus just four houses with willow?[/caption]

Use of ADR certified trailers

The use of ADR certified trailers for storing and moving gas by road represents the most efficient means of conveying the gas to the gas network and consumer. The other alternative of building large AD facilities on the gas network was evaluated and found to be costlier, and would have required excessive vehicle movements. Moving an energy dense gas makes more financial and operational sense, and it is a model better suited to the agri-sector, not too dissimilar to the creamery collection model. In comparison to moving solid biomass fuel by road, the composite gas trailers are much lighter and more compact than wood biomass trailers and the road movements are about a quarter of what would be required for moving solid fuel. Following this demonstration project, GNI is partnering with Ballyhoura Development and Renewable Gas Forum Ireland (RGFI) for the next project which will be a larger scale showcase project with a catchment area covering east Cork – Tipperary – Limerick. This hub facility will accommodate 30 AD facilities or more, and currently the project has engaged 14 initial farmer developers. AD facilities can be easily understood and managed by farmers. The on-site gas purification facilities require gas engineering competency, and present an opportunity for engineers, technicians and service providers in this field. Parties interested in gaining information or access to project opportunities in this area are encouraged to join the RGFI at www.renewablegasforum.com. RGFI holds monthly meetings in Portlaoise and organises regular workshops and training support services for its members on key topics such as safety assessments, biogas feedstock and AD operation best practices, certification compliance, etc. RGFI is affiliated with the European Biogas Association (EBA) and the European Renewable Gas Register (ERGaR).

The market and applications

The Gas Network gives renewable gas access to a ready market of nearly 700,000 consumers in Ireland across the three main sectors of heat, electricity generation, and transport. The gas network is 100 per cent efficient in conveying gas from source to consumer and is also an energy store, where gas is available and dispatchable on demand. This is a key feature that distinguishes it from the electricity network which cannot store energy. Ireland’s gas network has a storage capacity well in excess of one million Tesla power walls. Gas is the most efficient fuel for Heat and Combined Heat & Power (CHP) applications, and is also the most efficient fuel for central electricity generation, so renewable gas is a competitive alternative for decarbonising both applications. Much focus of national policy has been to decarbonise central power generation with solid biomass from short rotation crops such as Willow. The second illustration highlights that willow (or other forestation for fuel applications) are considerable less efficient that production of renewable gas from grass silage, which has more than 50 per cent higher annualised energy output value that willow.

Double the efficiency of solid fuel power generation

Added to this, existing national combined cycle gas turbine (CCGT) power plants are nearly double the efficiency of solid fuel power generation. This means that more than double the energy can be delivered for half the land utilisation. Given also that Irish farmers are all experienced grassland farmers, then no change is required in outputting grass silage compared with a permanent change to forestry which would yield lower output and income. The carbon lifecycle for grass to gas is also a matter of months, whereas wood biomass is a matter of years (minimum four years, and up to 75 years) and wood biomass also has significant carbon and harmful particulate matter emissions not present in gas burning applications. For transport applications, renewable gas can be produced and brought to market at a price that is lower than the diesel price equivalent. Until this market develops however, this represents a future growth area rather than a current market. Author: Ian Kilgallon is business development manager, Gas Networks Ireland. In the gas industry for more than 14 years, he has previously held the positions of national metering manager; market operations manager; regulatory affairs and key account manager. Before that, he spent 18 years establishing and supporting manufacturing operations across Europe, Asia and North America for Apple, EMC and Dell.