Proceedings

Developing Sludge Destruction, CRC or ROC’s?

Hunt, P. and Tze Yen, C., AECOM design Build

(free)

Abstract:

The implementation of the Carbon Reduction Commitment, CRC, has placed considerable pressure on the water utilities to look at and reduce their carbon footprint. It is has been agreed in the current OFWAT determination that the amount of renewable energy generated will rise from 742 GW h (08/09) to 965 GW h by the end of the AMP 5 period, a 30% increase .OFWAT included a figure of £57 x 106 in their final determination for renewable energy

One of the ways in which the utilities will achieve this increase in renewable energy is via anaerobic digestion. It is anticipated that up to 75% of sludge generated will be treated anaerobically to meet this increased requirement for renewable energy generation.

There are a number of new sludge destruction technologies under development which may be effective alternatives to established enhanced digestion technologies. Utilities may wish to consider using these if they do not have suitable sludge, space or budgetary conditions for the more established technologies. The regulatory regime under which the utilities may choose to claim the benefit is complex. There is a choice to be made between Renewable Obligation Certificates (ROC’s) or the Carbon Reduction Commitment (CRC) for renewable energy. In order to make this choice, utilities will have to carry out an economic analysis of processes, in order to determine the benefit achievable and process viability.

This paper looks at six such technologies and carries out an economic analysis in terms of ROC’s and CRC and whether to utilise gas for heating and /or electricity generation from increasing gas yield from improved SAS destruction when retrofitted to a digester.

Keywords

Carbon, footprints reduction and control

Introduction

The implementation of the Carbon Reduction Commitment (CRC) has placed considerable pressure on the water utilities to look at and reduce their carbon footprint. It is has been agreed in the current OFWAT determination that the amount of renewable energy generated will rise from 742 GWh (08/09) to 965 GWh by the end of the AMP 5 period, a 30% increase. OFWAT included a figure of £57 million in their final determination for renewable energy

One of the ways in which the utilities will achieve this increase in renewable energy is via anaerobic digestion (AD). It is anticipated that up to 75% of sludge generated will be treated anaerobically to meet this increased requirement for renewable energy generation. However, existing conventional digestion plants are known to be operating below their full potential, achieving biogas yields in the typical range of 0.8-1.0 m3/kg volatile solids (VS) destroyed. A number of new sludge destruction technologies under development have shown the potential to increase the digestion performance in terms of biogas production and volatile solids destruction to 0.9-1.2 m3/kg volatile solids (VS).

The Renewable Energy Obligation (REO) was introduced in the UK in 2002 to comply with the Renewable Energy Directive and aimed to reduce the environmental impact of electricity generation by increasing the proportion of electricity derived from non-fossil fuels. In 2005, 1.3% of the energy consumed in the UK was from renewable sources but this must be increased by 2020 to at least 15% (RED, 2009). The UK renewables strategy seeks to extend and expand the renewables obligation to ensure that over 30% of electricity is produced from renewable sources by 2020. The Renewables Obligation Order (ROO) replaced the REO in 2009. The revised legislation introduced technology “bands” that will be receive different varying awards of ROCs per MWh of electricity generated. The award is based on the track record of the technology and investment in emerging waste treatment technologies such as gasification, pyrolysis, and anaerobic digestion is being encouraged by awarding double ROCs. The ROC covers all electricity produced from renewable energy technologies with an output of over 5MW. Anything under 5MW is covered by the ‘feed-in’ tariff. There is speculation that eventually this will merge into one scheme covering all renewable energy.

An alternative economic incentive for generating renewable energy from anaerobic digestion from sewage sludge is the costs associated with carbon savings achieved through the Carbon Reduction Commitment (CRC) Energy Efficiency Scheme. The CRC scheme is set to require over 5,000 organisations operating within the UK in the public and private sectors, to internalise the cost of carbon emissions by putting a price on every tonne of carbon emitted (initially at £12/tonne CO2 emitted) as a result of their activities. Under the regulations, an organisation cannot claim a CRC benefit if they are claiming under the ‘feed-in’ tariff as this is seen as ‘double counting’.

In order to make this choice between ROC’s or CRC for renewable energy, an economic analysis of processes, in order to determine the benefit achievable and process viability will need to be undertaken. This paper looks at six such technologies and carries out an economic analysis in terms of ROC’s and CRC and whether to utilise gas for heating and /or electricity generation (see Fig 1).

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