• To identify optimum types, sizes and distribution of urban thermal energy recovery plant using an LCA approach;

• To investigate the potential for pyrolysis and gasification plants to provide decentralised power which could link to future energy requirements and changes in infrastructure;

• To bring together a database of information on energy from waste options in the urban environment for future planning of recovery

Description and Methodology
The overall aim of this project is to investigate the relative sustainability of alternative approaches to thermal processing of urban wastes, with a particular focus on recovery of value in the form of energy products from smaller-scale plant integrated into the urban environment. Through application of a general modelling framework, it is intended to link technology development and assessment activities within the Consortium programme through common questions about the contributions that different options may make to meeting various objectives for urban areas.

Assessment Strategy
The project will adopt a cradle-to-grave or life cycle approach, with a primary system boundary set at the point at which a material is designated as waste: from that point, collection, transportation, processing, thermal treatment, and residue management processes will be analysed, together with the production of useful energy and/or material products. Across these stages, the project will address the engineering costs and benefits, the environmental emissions implications and the changes in urban development and infrastructure patterns (through which public acceptability is often influenced). This is a large task as the range of activities is great. Much research has already been done in many areas, however, for example through the waste LCA tools developed by the Environment Agency. The innovations are to bring these materials together in a framework of relevance to urban development and focusing on the emerging range of smaller-scale thermal treatment techniques, with associated and diverse ranges of energy products.
The starting points for technologies to be investigated will be conventional large-scale incineration for energy recovery. For alternative approaches, thermal treatment through smaller-scale pyrolysis and gasification plant will be the primary focus.  These plants represent a step change in treatment scale, with associated impacts on the urban environment within which they would be sited. Their range of emissions and final energy products are different and it may also be appropriate to consider some combinations of gasification plant with electricity generator (eg small-scale plants with gas turbines or fuel cells; large-scale cogeneration plants with combined gas and steam turbines).
Pyrolysis and gasification are capable of producing liquid and gaseous fuels from a variety of feedstocks, with lower emissions and at significantly smaller economic scale than conventional large-scale incineration. The variety of energy vectors produced opens up potentially valuable markets for both decentralised stationary power and transport. These technologies could enable waste (and waste-biomass) management to link into a future hydrogen economy and urban infrastructure. Given the smaller economic scale of these technologies and their possible fuel flexibility, the prospects for integrating energy recovering with waste segregation, materials recovery and minimisation are much improved, as are the possibilities for co-combustion with biomass residues or crops. These characteristics imply a wide range of potential effects on urban infrastructure and service provision, whose assessment requires an interdisciplinary systems analysis approach. The project will investigate the suitable size(s) of energy recovery plant through a range of assessment criteria applied to specified technology scenarios. For promising options, the project will investigate the economic aspects involved in the construction of a pilot scale facility and will include market assessments focused on the energy products.
The assessment process described above will be based upon engineering knowledge and an experimental programme that will provide information on the performance of the alternative technology options across the individual steps that may be involved: a) waste segregation, b) shredding, c) pyrolysis, d) gasification, e) combustion, f) power generation, g) gas cooling, h) flue gas cleaning, i) liquid and/ or solid effluent disposal.  The efficiency, cost, maintainability, operability and emissions of each step are the basic data required. The experimental programme is broadly divided into three stages, to investigate for each treatment approach:  i) the suitability of different waste and virgin biomass feedstocks, and thus the implications for the wastestream to be treated;  ii)  the performance of the thermal treatment processes themselves;  iii)  the nature of energy products produced, including chars suitable for use in a further combustion or gasification stage. Development of the assessment strategy will carried out by IC, with main data inputs provided by Sheffield and minor inputs from other partners.

Pyrolysis and gasification treatment: The focus will be on the application of fluidisation technology to optimise the potential for generating energy from renewable sources and for improving waste management systems. The work will investigate current fluidised bed process technologies employed for the production of energy from thermal treatment of waste-derived fuels. The project will provide a comprehensive assessment of the fluid-bed reactor types and operational process conditions for the various thermal treatments, namely combustion, pyrolysis and gasification.
The engineering study will highlight the implications of the different technologies for air pollution, the treatment of the output gas streams and the consequent production of thermal and electric energy. This will lead to consideration of the application of novel breakthrough fluidised beds technologies based on flameless combustion (high temperature gasification using NASA technology on Plasma Arch Torches) for the urban production of clean electric energy. Part of this work will involve liaison with an industrial collaborator involved in the design and construction of the first waste gasification plant in Europe based on plasma arch technology. For the most promising options, the project will also investigate the possible scale of the plant, examining the use of fuel cells or small gas turbines and also cogeneration plants, and the economic aspects involved in the construction of a pilot scale facility. Within this framework, the project will provide an assessment of the market focused on the energy products and will formulate engineering strategies for innovations in future sustainable waste process developments. . UCL will be responsible for the engineering feasibility study of different existing and novel technologies using fluidized beds. In collaboration with IC and through the London Business School, UCL will also be responsible for the feasibility study on plant scales.

Experimental programme

Wastestream composition and waste segregation: Recent developments in national recycling and reuse programmes have led to segregation of an increasing proportion of waste to enhance material recovery. Several of the segregated streams contain material that cannot viably be reused or recycled, however, and this project will address the efficient recovery of energy from this new source. Physical and chemical characterisation of the material for treatment represents a key element of this work, and significant insight will be provided by a rigorous study on the waste mix, taking into account the likely impact of current and forthcoming legislation on waste compositions. The work on wastestream composition and waste segregation will be carried out by Sheffield.

Energy products from thermal treatment: Since energy is more valuable in the form of electricity than as heat, a major use of wastes will be for electricity production with CHP.  Expertise derived from earlier involvement with the Sheffield CHP scheme will be very relevant here.  Efficient generation systems generally require clean gaseous (or liquid) fuels.  Thus the nature of transformed fuels must also be matched to the chosen combustor.  In addition, the process design of appropriate gas cleaning treatment must be incorporated in this study.  Experimental work will be required to ascertain the combustion/gasification characteristics and (flue) gas treatment for the new forms of feed material that will emerge from new waste segregation schemes. The novel technologies to be investigated and developed within this programme have different characteristics from conventional incinerators and it is appropriate to assess the scaling features of their technologies within this project.  A further characteristic of pyrolysis is the ability to produce a range of secondary fuels, primarily chars of different characters which may be conveniently stored and used for CHP. Pyrolysis processes have been used for a long time in charcoal production, and slow pyrolysis can maximise the solid char yield, but potential problems caused by tars must be addressed.  It should be noted that the form of the carbon (e.g. amorphous or graphitic) has a dramatic effect on its behaviour during combustion or gasification.  Therefore the physical form of the char will have to be changed to match the needs of subsequent processes. A separate project is planned for submission to EPSRC responsive mode, concerning characterisation of the physical and chemical properties of both powdered and pelletised MSW char and their performance as an energy fuel in both fixed and fluid-bed gasifiers. Analysis of these secondary fuels will be included in the assessment of appropriate technologies for recovery of energy from waste.

This work will be carried out by Sheffield, with input from IC on scaling features of the technologies.

Deliverables
Deliverables from the project will include:

1. Matrix tables listing, for each conventional and new technology, the value of key parameters (eg process efficiency, cost, operability, emissions) for stages of the waste treatment chain. These will form the basis of the analytical study comparing the economics and environmental features of each technology, but also represent a significant output in their own right.

2. Technical scenarios for different scales and locations possible and appropriate for different fluidized bed process plant (eg small/urban, medium/peri-urban, large/ex-urban). These will form the basis for assessment work, as well as representing an analysis of the current state-of-the-art for urban thermal waste treatment.

3. A characterisation of the effects of process scale (eg. on economics; on the options for CHP and/or district heating; on impact of air emissions; on planning issues and public perceptions) according to quantified indicators (eg cost per tonne waste treated and emissions profiles) and qualitative interpretation of urban and social impacts.

4. An analysis of the technical and practical prospects for the emerging technologies, and the consequences for the waste management associated with urban areas.

5. Interpretation of the overall conclusions in terms of EU and UK legislation, bearing in mind anticipated developments in policy and regulation in the next decade that are likely to strengthen the requirements for source separation, value recovery and carbon emission reduction.

Contributions to Waste Consortium Headline Objectives
The research will allow a clearer understanding of waste management policy driver.  It will develop appropriate criteria to be used in assessing different approaches, and will contribute a greater understanding of the impacts of different energy recovery techniques/scenarios against these criteria, aiding development of sustainable and appropriate choices. In the longer term, the improved understanding described will help guide investment and research efforts in the development of appropriate technical solutions and/or societal/economic responses to the challenges faced.

For further information about this project, please contact Dr. Matt Leach