Reduction of flaring of biogas in anaerobic digestion plant 

Kathryn Richardson, Area Environment Manager with the Environment Agency, described their work with a biowaste operator, NWG Bioenergy Ltd, to reduce their emissions from a crop fed anaerobic digestion plant in West Yorkshire. At this site the Environment Agency’s intervention resulted in a reduction of unburnt biogas being vented as well as minimising the use of the flare.  

What is the regulatory role of the Environment Agency? 

We work to create better places for people and wildlife, and support sustainable development. Part of the role of the Environment Agency is to regulate major industry and waste. Our priorities are to work with businesses and other organisations to manage the use of resources and to work as a regulator to protect people and the environment and support sustainable growth. 

Biowaste is a growing and developing sector and we regulate a diverse portfolio – anaerobic digestion for food waste and on farms plus compost sites and more. The regulation of waste through permitting controls and site inspections drives the reduction of greenhouse gas emissions.  

Why was this work necessary? 

NWG Bioenergy Ltd were flaring up to 20% of the biogas that they were producing, which should have been going into the gas network for utilisation. 

By working with the operator we collected information on the amount of biogas being flared, biomethane to grid, total biogas and the target for biomethane to grid. 

It was apparent that the site had been regularly using the flare for a number of reasons that could have been avoided due to better infrastructure and management. The site only had 30 minutes of gas storage so where Northern Gas Networks (NGN) network capacity constraints prevented gas from being injected for periods longer than 30 minutes, the flare was used.  In addition, the flare was being used when there were problems with gas upgrading and the NGN gas specifications were not met, or difficulties not resolved within 30 minutes.  

Who worked together to overcome these difficulties?

NWG Bioenergy Ltd were committed to this challenge and worked with equipment suppliers, consultants and Northern Gas Networks to develop design improvements whilst meeting all relevant gas safety regulations.   All stakeholders were committed to find a solution because of the environmental benefit and opportunity to significantly reduce carbon impact.  

How were these challenges overcome?

These instances could have been avoided if on site gas storage was increased or there was a different outlet for the gas – combined heat and power (CHP) with export of electricity to grid, for example. However, these options required further infrastructure being installed (and carbon usage).  

So, the operator came up with a different way of measuring gas pressure prior to injection and improved their management of the plant - which had the result of reducing flare usage by up to 15%. The design improvement involved relocating a critical pressure sensor closer to the connection with Northern Gas Networks, therefore avoiding any inherent pressure losses diverting flows prematurely. 

The modification was completely successful and Northern Gas Networks have not rejected flows due to high pressure since this improvement was implemented. 

What were the commercial and environmental benefits of this work? 

This utilisation of the gas resulted in a significant reduction in greenhouse gases to the environment, improved compliance and increased revenue for the company. It has reduced environmental impact and improved gas to grid resulting in increased revenue. 

How much has this case study reduced carbon emissions? 

Overall impact of this gas to grid plant improvement is 1,920,439kg CO2e savings (annually); 20% flaring itself contributed 327,000 kg CO2e. 

Saving almost 2 million kg CO2e is something that the whole team are incredibly proud about. 

What unexpected benefits were there? 

There is better gas to grid stability due to not diverting flows, with fewer breakdowns due to reduced gas upgrade plant shutdowns. 

What are the EA’s future plans in this sector? 

As part of our wider regulatory work, our priorities for the biowaste sector include a focus on plastic removal from digestate and recovery of energy from biosolids. 

What would help others across Yorkshire and Humber to replicate your success? 

An Anaerobic Digestion Operator User Group to be set up to share experiences and ideas. Work closely with regulators (EA), Users and Northern Gas Networks to share ideas and risks; and learn best practise from other operators.