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EPSRC THERMAL MANAGEMENT

OF INDUSTRIAL PROCESSES

Case Study: Sheffield District Heating

(December 2010) Report Prepared by:

SUWIC, Sheffield University

Researcher: Dr Q. Chen

Investigators: Professor Jim Swithenbank Professor Vida N Sharifi

Sheffield University Waste Incineration Centre (SUWIC) Department of Chemical and Biological Engineering Sheffield University

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Executive Summary

Energy sustainability and greenhouse gas emissions have become critical

international social issues. Among all the state-of-the-art technologies, combined

heat and power (CHP) can help address both issues with efficiency better than

separate heating and electrical generating plants. Sheffield district heating network

is one of the largest and most successful CHP schemes operating in the UK. By

harnessing the energy from this local energy recovery facility, the district heating

system provides an economical, low carbon and environmentally friendly heat source

to businesses; householders and local authority in Sheffield.

In accordance with our EPSRC grant proposal, Sheffield University has carried out

a techno-economic feasibility study of Sheffield District Heating system. Two key

parameters were investigated: i) energy efficiency and ii) reduction in CO2 emissions.

Some main findings from this study are as follows:

1. By reclaiming a certain amount of the by-product heat for heating purposes,

combined heat and power technology can achieve the energy thermal

efficiency higher than 75%. Recovery of energy from MSW for heat and

power generation can reduce the CO2 emissions by around 70,000 tonnes per

year.

2. The recovery of low grade latent heat from water vapour in the flue gas can

greatly increase the thermal efficiency of the CHP plant from 75% to 93%. It

is possible to achieve higher efficiencies if the temperature of return water

temperature in the system is lowered to about 30C. Condensation of flue gas

not only helps to recover certain amount of low grade latent heat, but also

saves up to 90,000 tonnes of CO2 emissions per year.

3. Solid Recovered Fuel (SRF) and Refuse Derived Fuel (RDF) have much better

fuel qualities (e.g. calorific value) when compared to Municipal Solid Waste

(MSW). The electrical and thermal efficiencies of SRF-fired CHP systems

are higher than those of MSW-fired plants. The net CO2 emission reduction

by SRF (80,000tonnes/year) is greater than those by MSW in a CHP system.

4. A simplified cost analysis is performed to evaluate potential benefits for an

MSW fired CHP/DH system using SRF as a fuel. The capital cost for the

proposed MBT facility is around €57.3 million. Given no time value of

money, the payback period for this replacement is approximately 13 years.

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List of Contents

1. Introduction ............................................................................................................1

1.1 CHP and District Heating .............................................................................1

1.2 Solid Recovered Fuel....................................................................................5

2. Sheffield District Heating System ..........................................................................9

2.1 Energy-from-Waste System..........................................................................9

2.2 District Heating Scheme.............................................................................11

2.3 Emissions....................................................................................................12

3. Scenario Analysis .................................................................................................14

3.1 Base Cases: Fossil Fuel Fired Power Generation and Heating Systems ....15

3.1.1 Case I-A: Coal-fired Power Plant ....................................................15

3.1.2 Case I-B: Gas-fired Condensing Boiler for Residential Heating ....17

3.2 Case II: MSW-fired CHP System ...............................................................18

3.3 Case III: SRF-fired CHP System................................................................20

3.4 Efficiencies of Energy Conversion and Utilisation ....................................21

3.5 Environmental Impacts...............................................................................23

3.5.1 Reduction in CO2 Emission (Energy Recovery from MSW) ..........23

3.5.2 Reduction in CO2 Emission (Energy Recovery from SRF).............24

3.5.3 Influence of Flue Gas Condensation on CO2 Emissions .................24

3.5.4 Impacts on Other Flue Gas Emissions.............................................25

3.6 Economic Analysis .....................................................................................27

3.6.1 Capital Cost of MBT Facility for SRF Production..........................28

3.6.2 OPEX and CAPEX for SRF Production..........................................28

3.6.3 Benefits ............................................................................................28

4. References ............................................................................................................31

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1. Introduction

Energy sustainability and greenhouse gas emissions have become critical

international social issues. Energy demand across the world continues to grow in

long term. The effect of energy production and usage on the global environment has

triggered increasing concerns worldwide. To address these issues, alternative energy

sources and technologies have gradually attracted more and more attention.

Governments target for reductions in carbon dioxide emissions and an increase in

the percentage of electricity generated by renewables. For example, the UK

government has published its Low Carbon Transition Plan, which sets out how the

UK will cut CO2 emissions by 34% of 1990 levels by 2020 and at least 80% by 2050

(HM Government, 2009). In this plan, the government expects 40% of the power

used in 2020 to come from low carbon sources – 30% from renewables, the rest from

nuclear (including new build) and clean coal. For homes and communities, around

15% of the yearly emission cuts between now and 2020 will be achieved by making

homes more efficient and supporting small scale renewable energy.

Among all the state-of-the-art technologies, combined heat and power (CHP) can

achieve both targets with efficiency better than separate heating and electrical

generating plant. District heating supplied by a CHP plant increases the overall

thermal efficiency from approximately 50% for the best electricity generating plants

(CCGTs) to approximately 85% for a CHP plant. This can potentially reduce CO2

emission by 30%. On the other hand, municipal solid waste (MSW) generally

represents almost 20% of the total energy needs of a city. Therefore, when MSW is

used as fuel for a CHP plant, the combination can contribute a major reduction to net

CO2 emissions.

1.1 CHP and District Heating

The EU Cogeneration Directive (EU 2004) defines CHP as delivering minimum

levels of primary energy savings, with savings of 10% required for most CHP capacity.

This legal requirement, which must be met to qualify for most forms of public support,

is enacted in the UK through the CHP Quality Assurance (CHPQA) programme

(CHPA 2010). Generally, CHP systems are based predominantly upon existing,

proven power generation technologies: steam turbines, gas turbines and reciprocating

engines used the world over to generate energy. This use and adaptation of existing

technology not only contributes to the relatively low cost of CHP, but also ensures

that it is a proven and reliable technology, capable of delivering an immediate impact

in transforming our energy system. Connected to a district heating network, CHP

can provide heat and power to multiple customers in city centres, towns, villages,

industrial zones and other built environments with a dense ‘heat load’, this being a

high concentrated demand for heat. Up to 2007, over 4,000 CHP and district heating

utilities are operating in towns and cities across Europe.

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District heating is a convenient way to heating space and tap water. In many

processes, for example when electricity is generated or waste is burned, large parts of

the energy are set free in the form of surplus heat. The fundamental idea behind

modern district heating is to recycle this surplus heat which otherwise would be

wasted- from electricity production, from fuel and biofuel-refining, and from different

industrial processes.

A district heating system is essentially composed of a network of insulated pipes

used to deliver heat, in the form of hot water or steam, from the point of generation

(source) to an end user. The network provides a means to transport heat efficiently.

The carrier pipe system is mainly of steel but other materials such as plastics are used.

The distance a network can reach is easily extended by simply adding more providers

of heat, or ‘heat sources’, along the way (CHPA 2010).

In addition to energy from fossil fuels, heat sources for district heating scheme

include,

• Waste heat from power generation.

• Heat produced by the incineration of municipal waste.

• Reject heat from process industries.

• Landfill gas extraction.

• Geothermal (hot rocks) and thermal springs.

• Biomass - Agricultural and Animal waste products.

• Heat pumps.

• Fuel cells and solar thermal arrays

The ability to integrate diverse energy sources implies that end users are

independent upon a single source of supply. This helps guarantee service reliability

and continuity of the system. District heating networks also have the ability to

balance the supply and generation of heat, across location and over time. Over the

course of the day, heat demand shifts between residential consumers to commercial,

industrial and public buildings and back again. A heat network can match and

manage these flows, whilst maximising the utilisation of the plant providing the heat.

Demand can also be managed across seasons, with networks supporting the operation

of distributed absorption cooling plants in the summer providing cooling on a

significant scale (CHPA 2010).

Heat sources can be either directly connected to the distribution system or indirectly

connected through a heat exchanger. The direct system is limited to use where water

is the distribution medium and where the water quality and pressure requirements are

the same for the heat source and the building’s internal distribution system. The

indirect connection allows the heat source and the distribution system to be operated

as separate systems with different temperature and pressures, allowing more design

flexibility for both systems.

The district heating medium (steam or hot water) is distributed from the heat source

through supply pipes to the end users interface and is returned after heat has been

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extracted. Delivery is accomplished by circulating pumps which create a pressure

differential between the supply and return pipes. Pumps are selected to overcome

the flow resistance in the supply and return pipes and also the pressure differential in

the customer installation at the end of the system or the index point. The use of

variable speed drives to control the pumps ensures that consumed power is

minimised.

Figure 1 illustrates the principle of variable pumping (Skagestad and Mildenstein

1999). In areas where the ground level varies dramatically, it is important to ensure

that a minimum pressure is maintained in the return pipe to avoid evaporation and

cavitation in equipment such as pumps and valves. Direct district heating systems

typically operate with flow and return temperatures of 85/65°C and pressures of

below 6 bar, and indirect systems with temperatures of 110/65°C and pressures of

below 16 bar. The greater the temperature-difference between the flow and return,

the lower the flow rate required.

Figure 1 District heating network pressure diagram

°°

Figure 2 Pipe diameters in relation to temperature difference

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In Figure 2, difference in pipe sizes is compared when operating with alternative

temperature differences for two heating capacities. The district heating operator will

seek to ensure that the secondary return water temperature is as low as possible to

minimise pumping. It is common practice to compensate the district heating

medium supply temperature. When the heating demand decreases, its supply

temperature should be decreased to reduce energy losses from the pipe system. By

this adjustment, the energy efficiency using low-grade heat sources can be increased.

Figure 3 presents a typical example showing the variations in the supply temperature

depending on the outdoor temperature.

Figure 3 District heating compensation curve of the supply temperature

For the pipe networks, there are a number of different types of pipe material

available on the market. The vast majority of systems are based on pre-insulated

steel pipes. In smaller dimensions, the media pipe may be made of stiff or flexible

plastic pipes. The district heating medium supply temperature is often limited by the

type of pipework used. A common supply temperature range is 85 to 120°C. The

low end of the range is normally the temperature required to meet domestic hot water

needs during the summer. Pressures can go up to 25 bar but the majority operates

with a maximum pressure of 16 bar, while 25 bar is common in transmission systems.

By reducing the normal operating temperature and by reducing the effects of pressure

fluctuations, the life of the pipework can increase dramatically. Figure 4 illustrates

this phenomenon.

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Figure 4 Relationship between expected life of pipe and continuous operating

temperature

District heating can serve residential, public and commercial buildings as well as

meeting industrial demands for low-temperature heat. Building systems may be

connected directly or indirectly to a district heating distribution system. With a

direct connection, the heating medium is distributed within the building to directly

provide heat to terminal equipment such as radiators, unit heaters, etc. An indirect

connection uses a heat exchanger in the building to transfer the energy from the

district heating distribution system (primary system) to the building distribution

system (secondary system). The heat exchanger serves as an interface between the

district heating network and the building’s own radiator and hot water system.

There’s no boiler, no burning flame needed in the house and maintenance is taken

care of by professionals. Thus, compared to owning and operating an on-site boiler,

conversion to district heating can benefit the end users through increased reliability,

greater comfort, reduced investment, operating cost savings, increased energy

efficiency and greater fuel flexibility.

1.2 Solid Recovered Fuel

A major drawback to combustion of waste is that the fuel is likely to be

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non-homogenous, damp and it will come in large fragments. The water content will

lower the recoverable energy content per unit mass of fuel. The lack of homogeneity

will make for inconsistent combustion which will cause fluctuations in emissions

adding to the difficulty of cleanup, and it impedes designing for maximum efficiency.

In some cases, the combustion process often neglects materials recycling which

comes higher in the waste hierarchy, and so is not an ideal sustainable solution

(WMAA, 2003).

Turning waste into refuse derived fuel (RDF) or solid recovered fuels (SRF) is one

of the options available for waste treatment that can both reduce the volumes of waste

sent to landfill and simultaneously recover embodied energy from the waste material

(Arias-Garcia and Gleeson, 2009). SRF and RDF are fuels produced from

non-hazardous municipal solid waste (MSW) and commercial and industrial (C&I)

wastes. The term SRF is commonly used in place of RDF. SRF is a refined form

of RDF, intended for use in energy recovery facilities, which has been produced to

meet a standard published by the European Committee for Standardization (CEN)

standard, CEN/TS 15359. The specifications and classes are shown in Table 1.

Table 1 CEN/TS 15359 Solid recovered fuels – specifications and classes

The input waste can be production specific waste, municipal solid waste, industrial

waste, commercial waste, construction and demolition waste and sewage sludge.

SRF represents an interesting route to the development of CHP infrastructure. Some

of the benefits of SRF fired CHP are (Arias-Garcia and Gleeson, 2009):

� �the facilitation of an easier planning process,

� �increased overall energy efficiency,

� �flexibility of location, volume, security of supply, price and

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� the possible development of supply chain for waste wood disposal and

co-firing.

During SRF production, plants take bulk waste and remove recyclable or

non-combustible materials, the remainder then being dried and shredded or processed

into a uniform fuel. This fuel has a calorific value much higher than that for

municipal waste. SRF can take various forms including a loose or flock material,

which has been size-reduced or further densified to produce a fuel pellet, the final

form of SRF is dependent on the mode of energy recovery. Consequently, there are

many methods for producing SRF. These may include some or all of the following

processing systems: screening, air classification, dry, pelletising, magnetic recovery

(Wilen 2004, Chen et al. 2008).

Figure 5 Flow diagram of SRF production from household waste and commercial

waste (Wilen 2004)

Figure 5 presents a flow diagram of a typical SRF production plant. Roughly

source separated household waste passes through a fairly complicated production

process including operations like crushing, magnetic separators, screening,

eddy-current for non-magnetic materials, pneumatic separation and optic sorting.

The purpose is to separate the impurities (typically biowaste, glass, metals, aluminium,

PVC) as much as possible and to produce good quality SRF to be used in energy

recovery plants. As commercial waste generally contains little biowaste or fine

impurities, the sieving of the pre-crushed waste is usually bypassed (Wilen 2004).

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In general, SRF or RDF will burn in an incinerator cleaner and hotter. The process

will therefore be slightly more efficient and will need less of a cleanup operation.

RDF incineration is considered a more environmentally sound option for MSW

incineration, a life cycle analysis described by Ferrer et al. (2005) outlines RDF

incineration over mass burn as more favourable option: “Life cycle analysis favours

RDF combustion over mass burning because of the better environmental

performance”. The potential growth in RDF incineration is illustrated by future

plans for Finland, the National Waste Management Plan shown abandonment of mass

burn method and unsorted MSW to Landfill, instead focusing on source separation,

resource recovery and the utilisation of RDF (Strafford 2006).

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2. Sheffield District Heating System

Sheffield district heating network is one of the largest and most successful CHP

schemes operating in the UK. It has been developed around a municipal solid waste

(MSW) incinerator located close to the city centre since 1988. By harnessing the

energy from this local energy recovery facility, the district heating system provides an

economical, low carbon and environmentally friendly heat source to businesses;

householders and local authority in Sheffield. It is built using the latest technology

and is designed to maximise the efficient generation of combined heat and power for

the city’s residents (Veolia, 2010).

On average, Sheffield residents produce over 240,000 tonnes of waste every year.

Non-recycled waste collected in Sheffield is taken to the energy recovery facility (i.e.

the MSW incinerator) of the district heating system where it is burnt at temperatures

of over 850°C in a specially controlled environment. A network of pressurised hot

water pipelines under the city is integrated with the incinerator to recover heat from

household waste. Owing to this innovation, the city sends a relatively low level of

waste to landfill compared to most other regions in the UK. In 2001, Veolia

Environmental Services singed a 35-year waste management contract with Sheffield

City Council and is responsible for maintaining the waste collection and plant

operation and services (Veolia, 2010).

2.1 Energy-from-Waste System

In Sheffield CHP system, the heat from MSW incineration is converted to steam

and used to generate electricity and for districting heating. The incinerator is

designed to handle 225,000 tonnes of municipal solid waste a year (Veolia, 2010).

Figure 6 shows the process flow diagram of the energy recovery system. Waste (1)

from households, local authority services and some local businesses is brought to the

energy recovery facility. It is tipped into a waste storage bunker (2). From the

bunker the waste is lifted into a feed hopper (3) by an overhead crane (fully automatic

grab loading crane) at a rate of 28 tonnes per hour. The hopper feeds the waste into

a single incineration unit where it is burned at temperatures in excess of 850°C. Gas

fired auxiliary burners are used to ensure that the correct temperature of 850°C is

reached before any waste can be fed into the incinerator (Veolia, 2010).

Above the incinerator, a large CNIM 4-pass vertical boiler (5) produces superheated

steam at 400°C. A condensing steam turbine (10) uses this 40bar steam to generate

electricity for the National Grid and to produce hot water (11) for the district energy

network. Pressure take-offs from the condensing steam turbine allow a variety of

combinations to be used to optimise the use of energy between heat and electricity.

Air cooled condensers, sized for full load rejection, allow the thermal cycle to be

completed with the minimum environmental impact (Veolia, 2010).

10

(a)

10

11

1010

1111

(b)

Figure 6 Process flow diagram of the energy from waste facility (Veolia, 2010)

Urea (4) is introduced to the furnace to treat NOx (Oxides of Nitrogen) emissions.

Lime and activated carbon (6) is introduced to neutralise the acidity of the flue gas

and adsorb other pollutants. The cooled flue gases pass through a filter house (7)

where the particulate (dust) is captured by 1760 filters. Particulate collected in this

process is then stored in a silo for separate disposal later. Cleaned gases (8) are then

released through the chimney. These gases are continuously monitored to ensure

they meet strict environmental regulations.

An electromagnetic overband separator (12) removes metal from the ash. The

metal is delivered to a local company for recycling. Ash (13) from the incineration

process goes into a bunker. Particulates removed from the filtering process are taken

to a process plant for treatment and then safe disposal.

Table 2 summarises some technical data for the MSW incineration plant.

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Table 2 Technical summary of the energy-from-waste system (Veolia, 2010)

Total plant capacity 225,000 tonne of MSW

Bunker storage capacity 2,700 tonne of MSW

Plant throughput rate 28 tonne/hr @ 9.21MJ/kg

72 MW

Grate Martin reciprocating, 5 rows, 13 steps

Steam flow rate 86 tonne/hr

Steam pressure 40 bar

Steam temperature 400 °C

Maximum electrical output 19 MW

Maximum thermal output 60 MW

Chimney height 75 m

Gas fired auxiliary burners 2 × 20 MW

2.2 District Heating Scheme

At Sheffield CHP system, the plant generates up to 19MW of electricity for the

national grid, enough to power up to 22,600 homes. Up to 60MW of heat is supplied

to over 140 buildings connected to the district heating network so far. Currently,

these include 3 university campuses, 4 swimming pools, 3 theatres, 3 art galleries, 2

cinemas, 1 radio station, 1 glasshouse, 25 hotels, 21 private developments, other local

authority housing and corporate buildings, etc. Over 2,800 dwellings have benefited

from district energy in the Sheffield area. The flow diagram of the CHP system is

shown in Figure 7.

Figure 7 Flow diagram of the Sheffield CHP system (Veolia, 2010)

The district heating system provides buildings in Sheffield City centre and the

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surrounding areas with a low carbon energy source that is generated from MSW in a

central location, converted to hot water and pumped through a network of

underground pipes and delivered to a heat exchanger in buildings of all sizes and

types. There are currently 44km of pipeline installed across the city centre through

two networks. The system is supported by back-up facilities with 3 pre-heated

stand-by/peaking boiler stations ready to come on line at a moments notice with 84.6

MW of capacity. These back-up boiler stations consists of 5 gas and 4 oil-fired

boilers in total. Figure 8 shows schematically the process diagram of the district

heating system. In a typical year around 120,000 MWh of heat is delivered to

buildings in Sheffield City Centre and the surrounding areas. Table 3 summarises

the technical data for the district heating system (Veolia, 2010).

Figure 8 Districting heating scheme (Veolia, 2010)

Table 3 Technical data for the Sheffield district heating system (Veolia, 2010)

Hot water temperature 120 °C

Water pressure 16 bar

Pumps in the distributed pipework system 15

Capacity of backup boilers 87 MW

2.3 Emissions

The MSW incinerator is operating under the regulation of EU Waste Incineration

Directive and the Pollution Prevention and Control (PPC) regime (Defra 2009).

Table 4 presents the air emission limit values for the Sheffield CHP plant to meet.

The reference conditions are: temperature 0°C, pressure 101.3kPa and 11% oxygen

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dry gas. Figure 9 presents the monthly-averaged daily emission values from the

MSW incinerator. As can be seen, the missions are well below the limit values.

Table 4 Daily average emission limit values for the incinerator (Defra 2009)

Pollutant Emission limits Units

Dust 10 mg/m3

Total organic carbon (TOC) 10 mg/m3

HCl 10 mg/m3

CO 50 mg/m3

SO2 50 mg/m3

NOx 200 mg/m3

0

10

20

30

40

50

60

70

80

90

100

01/0

9

03/0

9

05/0

9

07/0

9

09/0

9

11/0

9

01/1

0

03/1

0

05/1

0

07/1

0

09/1

0

% o

f E

mis

sion

Lim

it

Dust

TOC

HCl

CO

SO2

NOx

Figure 9 Air emissions from the Sheffield CHP plant in recent years (Veolia, 2010)

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3. Scenario Analysis

Sheffield University has carried out a series of calculations (using Sheffield CHP

plant as a case study) in order to investigate the merits of CHP-DH (combined heat

and power generation with district heating). The application of low grade heat

recovery and use of SRF as a fuel were also considered. Some primarily economical

analysis was also conducted. Table 5 presents brief descriptions of all 3 cases.

Table 5 Summary of the case studies

Case Category Description

Base case A Coal-fired power generation system Based on Drax

Power Plant Case I

Base case B Residential gas-fired condensing boiler 30kW

A MSW-fired CHP system for power

generation only

B MSW-fired CHP system for heat supply

only

C MSW-fired CHP system for district

heating

Case II

D

MSW-fired CHP system for district

heating with lower return water

temperature

Case III SRF-fired CHP system for district

heating

Based on

Sheffield CHP

Plant

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Figure 10 CO2 emissions from SRF preparation, transportation and combustion

(Gaillarde 2008)

These cases can be compared with each other in terms of their contribution to the

greenhouse gas emissions from the plant. Only an assessment encompassing the

whole energy cycle − from conversion to delivery (thus including transportation) −

can give a realistic picture (Euroheat & Power 2007). However, as shown in Figure

10, CO2 emissions from the preparation and transportation of SRF are minor when

compared to emissions from SRF combustion. Therefore, in this work, only the

emissions from SRF combustion and related efficiencies were considered.

3.1 Base Cases: Fossil Fuel Fired Power Generation and

Heating Systems

As shown in Table 5, these two base cases are based on a coal-fired power plant and

a natural gas-fired residential heating boiler. The base cases correspond to separate

power generation and heating plants that are widely used throughout the world.

Energy efficiencies and CO2 emission factors were calculated as reference in this case

study.

3.1.1 Case I-A: Coal-fired Power Plant

This case is based on Drax Power Plant, the largest coal-fired power station in the

UK (Drax 2010). It consists of 6 power generating units. Each unit has a capacity

of 660MW, giving a total capacity of 3960MW. Although it is capable of co-firing

biomass and petcoke, coal is assumed to be the only fuel in this case study for the

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sake of simplicity.

Drax Power Station generates 7% of electrical power required by the UK. At full

output, it consumes around 36,000 tonnes of coal a day (Drax 2010). The coal fuel

comes from a mixture of both domestic and international sources, with domestic coal

coming from mines in Yorkshire, the Midlands and Scotland, and foreign supplies

coming from Australia, Colombia, Poland, Russia and South Africa. Each of the six

Babcock Power boilers supply superheated steam (16.6MPa and 563°C) to a steam

turbine set. Each steam turbine consists of one high pressure (HP) turbine, one

intermediate pressure (IP) turbine and three low pressure (LP) turbines. One HP

turbine generates 140MW of electricity. Exhaust steam (4.2MPa and 360°C) from

HP turbines is fed back to the boiler and reheated (4.02MPa and 565°C), then fed to

the 250MW IP turbines and finally passes through the 90MW LP turbines.

Table 6 presents assumptions used in the calculations. Table 7 gives the proximate

and ultimate analysis results (BCURA 2002) for the Daw Mill coal used in the plant.

The calculation results show that the electricity output is approx. 4000MWe and the

net electrical efficiency of the plant is around 33% correspondingly. As a result, the

CO2 emission factor for the power station is approx. 0.26kg/MJ (or 0.938kg/kWh).

In 2007, Drax produced 26.66TWh electricity in total (Drax 2007). Thus, based on

our calculations, the estimated CO2 emission from the plant was around 25 million

tonnes in 2007. This value is slightly higher than that reported by Drax, which was

22,160,000 tonnes in 2007 (Drax 2007). This overestimation could be due to the

difference in fuel composition and slight underestimation of the electrical efficiency

in the calculations.

Table 6 Main assumptions used in the Case I-A

Parameter Unit

Coal feed rate 1500 t/hr

Excess air 20 %

Thermal energy loss in the combustor 5 %

Main steam pressure 166 bar

Main steam temperature 563 °C

Turbine efficiency 85 %

Steam condenser pressure 0.05 bar

Temperature of flue gas exiting the boilers 140 °C

Table 7 Properties of the coal supplied by Daw Mill

Moisture 12.0

Volatile Matter 33.5

Ash 4.1

Proximate

analysis

(%ar)

Fixed Carbon 50.4

C 81.3 Ultimate

H 4.8

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O 11.5

N 1.3

analysis

(%, dry ash

free) S 1.1

NCV (MJ/kg) 28.9

3.1.2 Case I-B: Gas-fired Condensing Boiler for Residential Heating

Condensing boilers have now replaced most of conventional designs in powering

domestic central heating systems in Europe. In the UK, since 2005 all new gas

central-heating boilers fitted in England and Wales must be high-efficiency

condensing boilers. Condensing boilers are designed to capture a fraction of the

latent heat, i.e., the energy released by condensing water vapour in the flue gas. By

extracting this latent heat in the condensing boiler, the whole system can achieve

higher efficiency levels than non-condensing boilers. Typical models of condensing

boilers offer efficiencies around 90% (based on the lower heating value of fuels).

Case I-B is based on a 30kW domestic condensing boiler for residential heating.

Table 8 lists the assumptions made in the calculations. The fuel is natural gas with

its properties as shown in Table 9. In this case, the dew point of the flue gas is

approximately 56°C. The return water temperature is well below this dew point and

a portion of the water vapour latent heat can be recovered.

Table 8 Main assumptions used in the Case I-A

Parameter Unit

Heat input 30 kW

Fuel feed rate 3.25 m3/hr

Excess air 10 %

Thermal energy loss in the combustor 2 %

Return water temperature 40-45 °C

Temperature of flue gas exiting the boilers 50 °C

Table 9 Assumed composition of natural gas in Case I-B (Uniongas 2010)

Component Range Assumed value

Methane, vol% 95 87-96

Ethane, vol% 3 1.5-5.1

Nitrogen, vol% 2 0.7-5.6

Net calorific value, MJ/kg 44.7

Gross calorific value, MJ/kg 51.0

For this gas fired condensing boiler, the output heat capacity is 28.4kW. The

thermal efficiency thus reaches 94.9% (based on lower heating value) or 83.1%

(based on higher heating value of the fuel). The CO2 emission factor is

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approximately 0.06kg/MJ (or 0.23kg/kWh).

3.2 Case II: MSW-fired CHP System

In this case, a series of thermodynamic calculations were carried out to obtain mass

flow rates, temperatures and enthalpies for all the streams of the Sheffield CHP

System using heat and mass balances.

Table 10 lists the assumptions made for the calculations. Typical composition of

British MSW was used to represent the properties of MSW for Sheffield CHP plant,

as presented in Table 11. In the calculations, it was assumed that Sheffield CHP

plant had a net energy input of 72MWth. Calculations were conducted for four

different scenarios, namely,

� Case II-A: for electricity production only

� Case II-B: for district heating only

� Case II-C: combined heat and power for district heating

� Case II-D: combined heat and power for district heating with low return

water temperature

Table 10 Some assumptions used in the Case II

Scenario A B C D

Energy Input (based on LHV), MW 72 72 72 72

MSW feed rate, t/hr 30 30 30 30

Excess air, % 60 60 60 60

Main steam pressure, bar 40 - 40 40

Main steam temperature, °C 400 - 400 400

Turbine efficiency, % 85 - 85 85

Pressure of steam condenser or take-off for heating, bar 0.05 - 5 5

Steam temperature under the above pressure 32.8 - 151.8 151.8

Temperature of flue gas exiting the boilers, °C 120 120 120 35

Pressure of hot water for district heating, bar - 16 16 16

Temperature of hot water for district heating, °C - 120 120 120

Return water temperature, °C 65 65 30

Using the data presented in Tables 10 and 11, the electricity and/or thermal outputs

of the plant can be calculated for each of the four scenarios. In Case II-A where all

MSW is used to produce electricity, the total output is 19.0MWe with a net electrical

efficiency of 26.4%. In Case II-B where all MSW is burned to produce heat for

district heating, the thermal energy is approximately 60.3MWth with a thermal

efficiency of 83.7%. These outputs are identical to those listed in Table 2.

In the cases where both electricity and heat are produced, the electricity outputs are

19

both 7.94MWe (Cases II-C and II-D) and the electrical efficiencies are 11.0%. In

Case II-C, the thermal output for district heating is 47.5MWth. The thermal

efficiency is approximately 65.9%.

As MSW has the moisture content as high as 31%, the latent heat of water vapour in

the flue gas is quite high. This portion of low grade heat can be recovered using flue

gas condenser as additional energy source for district heating. However, the

operation of the flue gas condenser requires return water with low temperature below

the dew point of the flue gas (55.7°C). Therefore, in Case II-D, the temperature of

return water from the district heating system is only 30°C lower than in Case II-C.

The flue gas from the incinerator (or Energy-from-Waste system) is used to preheat

the return water. Thus, some latent heat in the flue gas can be recovered in this case.

As a result, the thermal output in Case II-D is 59.2MWth with the thermal efficiency

of 82.2%.

As MSW consists of hydrocarbons, combustion of MSW is also a source of CO2

emission. In all the four scenarios of Case II, the MSW feed rates are assumed to be

the same (30t/hr). Consequently, the emission rates of CO2 are identical (i.e.

24.3tonnes/hr ) for all the scenarios. In Case II-A where all MSW is used to produce

electricity, the CO2 emission factor is 0.355kg/MJ (or 1.28kg/kWh). In Case II-B

where all MSW is burned to produce heat for district heating, the CO2 emission factor

is 0.112kg/MJ (or 0.40kg/kWh).

20

Table 11 Typical composition of British MSW (Optimat 2001)

3.3 Case III: SRF-fired CHP System

In this case, the fuel for Sheffield CHP System is assumed to be SRF. Table 12

presents the fuel properties of RDF and SRF samples. As shown in Table 12, RDF

and SRF have much lower moisture content and ash content than MSW. The carbon

content and net calorific value of RDF and SRF are higher than MSW. As SRF is a

refined form of RDF, the moisture and ash contents of SRF are slightly lower than

RDF. Table 13 lists the conditions for the calculation in this case. Due to the low

moisture content in the SRF fuel, the water vapour fraction in the flue gas after SRF

combustion is also small. As the dew point of the flue gas is around 36°C, the latent

heat of water vapour in the flue gas is very difficult to recover to preheat the return

water from district heating system.

21

Table 12 Typical properties of RDF and SRF (Hernandez-Atonal et al. 2007; Dunnu

et al. 2009)

Sample (as received) RDF SRF

Moisture (%ar) 3.7 2.60

Volatile Matter (%ar) 67.6 77.8

Ash (%ar) 18.9 14.8

Fixed carbon (%ar) 9.8 4.8

C (%daf) 61.2 64.89

H (%daf) 8.2 10.04

O (%daf) 26.6 23.51

N (%daf) 1.3 1.05

S (%daf) 0.2 0.51

Cl (% daf) 2.5 -

NCV, MJ/kg 20.8 25.54

Table 13 Some assumptions used in the Case III

Energy Input (based on LHV), MW 72

SRF feed rate, t/hr 10.1

Excess air, % 120

Main steam pressure, bar 40

Main steam temperature, °C 400

Turbine efficiency, % 85

Pressure of steam condenser or take-off for heating, bar 0.5

Steam temperature under the above pressure 151.8

Temperature of flue gas exiting the boilers, °C 120

Pressure of hot water for district heating, bar 16

Temperature of hot water for district heating, °C 120

Return water temperature, °C 65

Based on mass and energy balances, the electricity output in this case is

approximately 8.4MWe, corresponding to an electrical efficiency of 11.7%. The heat

output for district heating is 50.4MWth and the thermal efficiency is thus 69.9%. In

this case, the CO2 emission rate is around 19.9t/hr.

3.4 Efficiencies of Energy Conversion and Utilisation

Figure 11 summarises the electrical and thermal efficiencies calculated for all

cases mentioned above. Cases I-B and II-B are two cases for heat production only.

The energy losses are mainly due to the flue gas released to the atmosphere. Hence

the thermal efficiencies for these two cases are well above 80%. As the gas-fired

boiler in Case I-B is working with flue gas condensing, the efficiency is extremely

high (around 93% based on LHV).

22

In Case I-A, as the parameters of superheated steam (temperature and pressure)

are higher than those in Cases II and III, the electrical efficiency is therefore the

highest among all the cases. In the cases of combined heat and power generation,

steam is taken off from the turbine under 5bar in order to reject heat at a fairly high

temperature to enable district heating. This lowers the overall plant electrical

efficiency to 11% in the cases Cases II-C and II-D from 26% in Case II-A where the

plant operates for electricity only.

However, in cases where only electric power is generated, a large amount of heat is

wasted and released to the atmosphere through cooling towers and flue gases. Thus,

a maximum 26-35% is achieved for the overall plant (electrical) efficiency in these

cases. By contrast, combined heat and power technology captures a certain amount

of by-product heat for heating purposes. Although the electrical efficiency is

inevitably reduced, the thermal efficiency is thus greatly increased. The overall

energy efficiencies of the plant in Cases II-C, II-D and III are above 75%.

0

10

20

30

40

50

60

70

80

90

100

Case I-A Case I-B Case II-A Case II-B Case II-C Case II-D Case III

Eff

icie

ncy

, %

Thermal efficiency

Electrical efficiency

Figure 11 Comparison of electrical and thermal efficiencies for all the cases

It should be noted that the recovery of low grade latent heat from water vapour in

the flue gas can greatly improve the thermal efficiency of the plant if the fuel has

fairly high moisture content. As shown in Case II-D, the total plant energy

efficiency is close to that from the domestic gas-fired condensing boiler. The

achievement of this high efficiency requires sufficient low temperature of return water

from district heating system.

23

3.5 Environmental Impacts

The CO2 emission rates and emission factors for all the cases are calculated and

summarised in Table 14, together with the electricity and heat outputs. It should be

noted that Case I is based on the combustion of fossil fuels whereas Cases II and III

are based on waste combustion. Based on the data from Case I, some

environmental impacts of MSW/SRF fired CHP are briefly discussed. The influence

of low grade latent heat recovery on CO2 emission reduction is also analysed.

Table 14 Summary of the calculation results for all the cases

Electricity, MWe Heat, MWth CO2, t/hr Emission factor, kg/MJ

Base case A 4000 - 3748 0.26 Case I

Base case B - 28.4 6.4×10-3

0.06

A 19 - 0.36

B - 60.3 0.11

C 7.94 47.5 - Case II

D 7.94 59.2

24.3

-

Case III 8.4 50.4 19.9 -

3.5.1 Savings in CO2 Emission (Energy Recovery from MSW)

As shown in Table 14, the emission factors (Cases II-A and B) from MSW-fired

power and heat generation appear to be higher than those from the coal-fired power

plant (Case I-A) and a gas-fired condensing boiler (Case I-B). However, various

assessments have shown that about 20-40% (depending strongly on the degree of

separate collection of paper and organic waste) of the carbon in MSW is derived from

fossil sources, e.g., plastics (as shown in Figure 12). The remainder is derived from

biomass and can be considered a renewable resource (IEA Bioenergy 2003).

Consequently, the non-renewable amount of CO2 emissions from MSW-fired power

generation (Case II-A) is approximately 0.14kg/MJ or 0.52kg/kWh (i.e. 40% of the

emission of 0.36 kg/MJ). Similarly, the non-renewable amount of CO2 emissions

from MSW-fired heat production (Case II-B) is about 0.04 kg/MJ or 0.16kg/kWh.

These values are thus less than the CO2 emission factors of the coal-fired power plant

(Case I-A) and the gas-fired condensing boiler (Case I-B).

Therefore, recovery of energy from MSW for power generation or heat production

produces a net reduction in greenhouse gas emissions. In Case II-A, the total CO2

emission reduction is 2.28kg/s, or over 70,000 tonnes per year. In Case II-B, the

saving in CO2 emission is thus 0.96kg/s, equivalent to approximately 30,000 tonnes

per year. In Case II-C where both power and heat are produced from MSW, the total

CO2 emission saving is 2.21kg/s, which equals around 69,000 tonnes/y.

24

20%

20%60%

Renewable (biomass derived)carbon - 60%

Variable fraction - 20%

Non-renewable (fossil derived)carbon - 20%

Figure 12 Sources of carbon content in MSW

The calculated values of CO2 emission reduction by no means take into account the

emissions from MSW landfill. As the energy in MSW is recovered for power and

heat generation, the emissions from traditional landfill are avoided. If the MSW was

consigned to landfill then about 70kg of methane (actual range 50-100kg) could be

released for each tonne of waste. Given the higher global warming potential of

methane, this is equivalent to 1610kg CO2 per tonne of MSW. In modern landfills

about half of the methane can be extracted and used for energy production, therefore

reducing the overall emissions (IEA Bioenergy 2003).

3.5.2 Savings in CO2 Emission (Energy Recovery from SRF)

Given the same energy input for the plant, SRF gives less CO2 emission rate than

MSW, as shown in Table 14. The renewable carbon content in SRF is about 50-55%

(Zucchelli 2009). Thus, the non-renewable CO2 emission in Case III is

approximately 9.55tonnes/hr. Consequently, the CO2 emission saving is 2.55kg/s

and the annual CO2 emission reduction is around 80,000tonnes.

3.5.3 Influence of Flue Gas Condensation on CO2 Emissions

As shown in Figure 11, low grade latent heat recovery in Case II-D has an

advantage in improving the overall thermal efficiency of the CHP system. This

therefore results in greater CO2 emission reduction than Case II-C. In Case II-D, the

saving in CO2 emission is 2.92kg/s. Thus, the annual CO2 reduction is

approximately 91,000tonnes.

Figure 13 summarises all the calculated savings in CO2 emissions for Cases II and

III. As shown, the net CO2 emission reduction by SRF is greater than those by

25

MSW in a CHP system. As flue gas condensation can recover certain amount of low

grade latent heat, it leads to a significant reduction in CO2 emissions of a system

which recovers energy from MSW.

0

10

20

30

40

50

60

70

80

90

100

Case II-A Case II-B Case II-C Case II-D Case III

Avoid

ed C

O2 e

mis

sions,

×10

3 t

onn

es

Figure 13 Comparison of avoided CO2 emissions among Cases II and III

3.5.4 Impacts on Other Flue Gas Emissions

In addition to the reduction of CO2 emission, another major benefit associated with

energy recovery from MSW is the reduction in emission of other gaseous pollutants.

Table 15 compares the ELVs of some key pollutants from large-scale power stations

with those from Waste Incineration Directive (WID). As can be seen, the ELVs for

MSW incinerators are more stringent than those for coal-fired power stations. Using

the best available techniques (BAT), the waste incineration industry has reduced its

emissions over the last ten years by a factor of 10 or more due to enhanced legislative

environmental controls (Last 2010). In particular, dioxin emissions have been

reduced to well below those of other combustion process under the regulation of the

WID.

Table 15 Emission limit values of some pollutants from large-scale coal fired power

plants (O2 reference concentration: 6%)

Pollutant Large-scale coal fired

power plants*

Derived ELVs for

incinerators**

Dust, mg/m3 50 15

Total organic carbon (TOC), mg/m3 - 15

26

HCl, mg/m3 - 15

CO, mg/m3 - 75

SO2, mg/m3 200 75

NOx, mg/m3 500 (200 after 2016) 300

* (EU 2001)

** Calculated from Table 4 from O2 ref. concentration of 11% to 6%

However, the Best Available Techniques (BAT) for flue gas treatment installed in

most recent industrial units built in Europe have emissions that are often significantly

lower than those imposed by law. Therefore, assuming that the emission factors

must be equal to emission limits appears to be too optimistic (Consonni et al 2005).

An up-to-date evaluation of environmental impacts can be achieved based on direct

measurements carried out on state-of-the-art combustors.

Tables 16 and 17 compare the emission factors from an Energy-from-Waste system

with those from a coal-fired power plant and a gas-fired boiler. As shown, the

emission factors of some pollutants, such as PM10, NOx, NMVOC, SO2 and HCl,

from MSW combustion are lower than those from coal combustion.

Table 16 Emission factors for a coal-fired power plant and a gas-fired boiler for

domestic heating (Giugliano et al. 2008)

Coal-fired power plant Gas-fired boiler for

domestic heating

CO2 g/kWh 759 238

CO mg/kWh 41 57.6

PM10 mg/kWh 130 0.36

NOx (as NO2) mg/kWh 1938 212.4

SOx (as SO2) mg/kWh 4399 3.6

N2O mg/kWh 3.0 3.6

HCl mg/kWh 133 -

HF mg/kWh 38 -

Cd µg/kWh 2.8 -

Hg µg/kWh 92 0.234

Pb µg/kWh 62 -

NMVOC mg/kWh 77 18

Dioxin (I-TEQ) pg/kWh 41 -

Table 17 Emission factors (EF) for Energy-from-Waste systems in Italy and calculated

EF for Cases II-A and B

EF from combustion

of 1tonne MSW*

Calculated EF based

on Case II-A**

Calculated EF based

on Case II-B**

CO2 (fossil) 425 kg/t MSW 671 g/kWh 334 g/kWh

27

SOx(as SO2) 49 g/t MSW 77 mg/kWh 38 mg/kWh

NMVOC 20 g/t MSW 32 mg/kWh 16 mg/kWh

NOx(as NO2) 855 g/t MSW 1350 mg/kWh 672 mg/kWh

PM10 12 g/t MSW 19 mg/kWh 9 mg/kWh

Dioxin(I-TEQ) 310 ng/t MSW 489 pg/kWh 244 pg/kWh

Cd 61 mg/t MSW 96 µg/kWh 48 µg/kWh

Hg 61 mg/t MSW 96 µg/kWh 48 µg/kWh

Pb 610 mg/t MSW 963 µg/kWh 479 µg/kWh

HF 4.3 g/t MSW 7 mg/kWh 3 mg/kWh

Ammonia 12 g/t MSW 19 mg/kWh 9 mg/kWh

HCl 43 g/t MSW 68 mg/kWh 34 mg/kWh

N2O 100 g/t MSW 158 mg/kWh 79 mg/kWh

CO 61 g/t MSW 96 mg/kWh 48 mg/kWh

* (Consonni et al 2005)

** Calculated from the 2nd

column based on the outputs from Cases II-A and B

3.6 Economic Analysis

Although the fuel quality of SRF or RDF is improved and makes for better more

efficient combustion, the cost of the process is a major drawback (Rudder et al. 2005).

It is a capitally intensive process which has to be done on a grand scale if it is ever to

pay off its costs. The process of sorting, drying and pelletising of MSW is costly

and time consuming. The use of RDF entails significant additional costs which can

only be commercially viable in plants of over 1,000 tonnes per day (Optimat 2001).

The sale of recyclable materials will go some way to generate revenue, but the current

state of the recycling market does not bode well for this. Often a RDF/SRF plant

operator will not have the revenue (or even expertise) to build an accompanying

incineration plant so will have to develop a business partnership in order to sell the

fuel. The payback period is long as costs are high; therefore revenue from sales has

to be guaranteed. This necessitates a guaranteed partnership with an incineration

company for an extended period in order for the plant to make profit (Cox et al.

2008).

A simplified cost analysis is performed in order to evaluate potential benefits for an

MSW fired CHP/DH system using SRF as a fuel. The cost analysis compares

financial cost entailed in purchasing necessary equipment for SRF production versus

financial benefits of recovering energy from SRF incineration. This is based on the

assumption that existing MSW collection, transportation and incinerator system do

not need to be upgraded or amended and thus no other financial costs are entailed.

The costs associated with this fuel replacement include initial purchase price of

machinery, operating and maintenance costs. As there is negligible difference in the

renewable biomass content between MSW and SRF, the loss of Renewable Obligation

28

Certificates (ROCs) can be neglected.

3.6.1 Capital Cost of MBT Facility for SRF Production

The principle of the MBT (Mechanical Biological Treatment) plant is to stabilise

and separate the residual waste stream into less harmful and / or more beneficial

output streams. MBT is a generic term for an integration of several processes (Last

2010). The processes are designed to handle raw “black bag” municipal waste (after

any source segregated recycling and composting has taken place) and tend to involve

a recycle recovery element (typically metals and glass) and drying/partial composting

of the remaining waste to produce a more stabilised residue. The recyclable

component may be extracted either prior to or post “stabilization”. The remainder of

the waste is screened/sorted and homogenised to produce either a feedstock for

another treatment process (e.g. RDF/SRF for energy recovery in a gasification,

co-incineration, or Energy from Waste plant) or may be sent to landfill as a partially

stabilised residue.

The capital cost (CS) for a whole MBT plant with MSW treatment capacity of

88,000tpa is approximately €27 million (Monson et al. 2007). The capital cost (CL)

of the MBT facility treating 240,000 tonnes of waste can be scaled with capacity (Cp)

power by an exponent 0.75 (Consonni et al. 2005), i.e.,

75.0

=

S

L

SLCp

CpCC

Hence, for the proposed MBT facility, its capital cost is around €57.3 million.

Generally, the conversion rate for MSW to SRF is about 50%. Thus the throughput

of SRF is 120,000 tpa. For such a scale of facility the land requirement is

approximately 3-4Ha (Last 2010).

3.6.2 OPEX and CAPEX for SRF Production

The operating and maintenance costs reported in literature appear to vary widely.

Monson et al. (2007) estimated the operating costs at €35-55/tonne SRF,

approximately half was spent on exhaust air treatment based on a case study in

Germany. Some technology suppliers’ figures show the operational cost to be

£10-35/tonne SRF. In addition, £42-100/tonne SRF of CAPEX should also be

considered for the MBT facility (Arias-Garcia and Gleeson, 2009).

3.6.3 Benefits

Potentially, the gate fee to a MBT facility for SRF production is different from that

to an incinerator. According to Waste & Resources Action Programme (2010), the

gate fees for existing incineration facilities range from £32 to £79 per tonne with a

29

median value of £49/tonne. The gate fee for MBT facilities is about £75/tonne.

Hence there maybe exist some profit due to the increase in the gate fee.

The major potential revenue received from replacing MSW with SRF is from sale of

the increased electricity and heat, as well as through the sale of recyclate collected

during MBT and remaining SRF fuel. Given that the NCV of SRF is 25.5MJ/kg, the

feeding rate of SRF is 10.1 t/hr. The annual consumption of SRF is about

88,000tonnes for combined power and heat production. The other 32,000tonnes

SRF remains for sale.

As shown in Table 14 (Cases II-C and III), replacing MSW with SRF increases the

electricity output by 0.46MWe and the heat by 2.9MWth. The incensement is

equivalent to approximately 4,000,000kWh of electricity and 25,000,000kWh of heat

every year. Given the purchase price of electricity is £0.072/kWh (Strafford 2006),

the profit for the additional electricity is about £288,000 per year. The price of

district heating could be as high as £0.20/kWh (Davies and Woods, 2009). The

additional heat thus exerts approximately £5,000,000 annually.

Table 18 Summary of the cost-benefit analysis

Item Reference cost or price

Costs

Capital costs 57,300,000 €

OPEX 3,000,000 £/year 25 £/tonne SRF

CAPEX 5,040,000 £/year 42 £/tonne SRF

Revenue

Gate fee 6,240,000 £/year 26 £/tonne MSW

Extra electricity 288,000 £/year 0.072 kWh

Extra heat 5,000,800 £/year 0.2 kWh

SRF sale 320,000 £/year 10 £/tonne SRF

In the existing UK market the users of waste-derived fuels demand and are able to

receive a gate fee in the range of £20 to £50 per tonne, irrespective of the quality or

energy value of the fuel (Cozens and Manson-Whitton, 2010). Cozens and

Manson-Whitton (2010) thus gave one informative price for SRF to be -£1.50/GJ or

-£30/tonne. However, there are already signs that the market is changing, with

continental users offering to pay a small cost per tonne, and UK producers exporting

SRF to continental users in the face of an increasing demand for the product (Cozens

and Manson-Whitton, 2010). In this case, the sale price of the remaining SRF

product is assumed to be £10/tonne, providing the transportation costs and gate fee

outweighed net benefits (Strafford 2006). Then the revenue from the left SRF is

about £320,000 per year.

Table 18 presents the costs and benefits of replacing MSW with SRF in an

MSW-fired system. For simplicity, if the time value of money is not taken into

30

account, the payback period of this replacement would be approximately 13 years. It

should be noted, however, there are also a number of risks associated with SRF

production, such as planning risks and the risk that the technology will not achieve the

performance levels. This could threaten the availability of the products as the

products would not meet the specification for end use and end up in Landfill

(Arias-Garcia and Gleeson, 2009).

31

4. References

Arias-Garcia, A., Gleeson, J. Solid recovered fuel regional assessments – Hull and

East Riding. RPS Planning & Development, JER7585, Jan. 2009

BCURA (The British Coal Utilisation Research Association). The BCURA Coal

Sample Bank: A Users Handbook. 2002.

Chen, Q., Swithenbank, J., Sharifi, V. Review of biomass and solid recovered fuel

(SRF) pelletisation technologies. Report for EPSRC SUPERGEN Bioenergy. 2008

CHPA (Combined Heat & Power Association), http://www.chpa.co.uk/, accessed in

November 2010.

Consonni, S., Giugliano, M., Grosso, M. Alternative strategies for energy recovery

from municipal solid waste – Part B: Emission and cost estimates. Waste Management.

2005, 25, 137-148.

Cox, M., Janssen-Jurkovicova, M., Nugteren, H. Combustion residues: current,

novel and renewable applications. John Wiley & Sons. 2008.

Cozens, P., Manson-Whitton, C. Bio-SNG: Feasibility study – Establishment of a

regional project. Progressive Energy Ltd. 2010.

Davies, G., Woods, P. The potential and costs of district heating networks: A report

to the Department of Energy and Climate Change. 2009.

Defra. Environmental Permitting Guidance: The Directive on the Incineration of

Waste. 2009.

Drax. Environmental Performance Review 2007.

Drax. Our history. http://www.draxgroup.plc.uk/aboutus/history/, accessed in

December 2010.

Dunnu, G., Maier, J., Hilbert, T., Scheffknecht, G. Characterisation of large solid

recovered fuel particles for direct co-firing in large PF power plants. Fuel. 2009, 88,

2403-2408.

EU (The European Parliament and the Council of the European Union). Directive

2001/80/EC on the limitation of emissions of certain pollutants into the air from large

combustion plants. Official Journal of the European Union. 27. 11. 2001. L309/1-21

EU (The European Parliament and the Council of the European Union). Directive

2004/8/EC on the promotion of cogeneration based on a useful heat demand in he

internal energy market and amending Directive 92/42/EEC. Official Journal of the

European Union. 21. 2. 2004. L52/50-60

Euroheat & Power. Treatment of district heating and cooling under rules for State

aid for environmental protection. 2007.

Ferrer, E., Aho, M., Silvennoinen, J., Nurminen, R. Fluidised bed combustion of

32

refuse-derived fuel in presence of protective coal ash. Fuel Processing Technology.

87(1), 2005, 33-44.

Gaillarde, E. Carbon footprint of solid recovered fuel. First UK Conference on

Solid Recovered Fuels. London, November 2008.

Giugliano, M., Grosso, M., Rigamonti, L. Energy recovery from municipal waste: A

case study for a middle-sized Italian district. Waste Management. 2008, 28, 39-50.

Hernandez-Atonal FD, Ryu C, Sharifi VN, Swithenbank J. Combustion of

refuse-derived fuel in a fluidised bed. Chem Eng Sci 2007; 62: 627-35.

HM Government. 2009. The UK Low Carbon Transition Plan: National strategy for

climate and energy. ISBN: 9780108508394

IEA Bioenergy. Municipal solid waste and its role in sustainability. 2003.

Last, S. Waste Technolgy: Energy from Waste (EfW).

http://www.mbt.landfill-site.com/EfW/efw.php, accessed in December 2010.

Monson, K.D., Esteves, S.R., Guwy, A.J., Dinsdale, R.M. Anaerobic Deigestion of

Centrally Segregated Biowastes - Case Study: Heilbronn (U-Plus UmweltService

AG) MBT Plant. The Wales Centre of Excellence for Anaerobic Degistion. 2007.

Optimat Limited. Co-utilisation of coal and municipal wastes. Report No. COAL

R212 DTI/Pub URN 01/1302. 2001.

Rudder, W., Keane, M., O’Sullivan, G., and Bischoff, R., 2005. Review of

Alternative Solid Waste Management Methods for GVRD. Prepared for the Greater

Vancouver Regional District (Burnaby, BC) by Earth Tech (Canada) Inc.

Strafford, A.J. A study into the economic, logistical and energetic potential to

condense household waste to form fuel. Earth & Environment. 2006, 2, 308-342.

Uniongas. Chemical Composition of Natural Gas.

http://www.uniongas.com/aboutus/aboutng/composition.asp, accessed in December

2010.

Veolia. http://www.veoliaenvironmentalservices.co.uk/sheffield/. Accessed in

November 2010.

Wilen, C. Review of waste processing technology for SRF. Report for IEA

Bioenergy Agreement – Task 36, 2004.

WMAA (Waste Management Association of Australia). Sustainability guide for

energy from waste (EfW) projects and proposals. 2003.

http://www.e-renewables.com/documents/Waste/Austrailia%20Sustainability%20Gui

de.pdf, accessed in Nov. 2010.

WRAP (Waste & Resources Action Programme). Comparing the cost of alternative

waste treatment options. Gate Fees Report 2010.

Zucchelli, L. The role of SRF for the Italian strategy in energy from waste.

International Technical Conference on “Solid Recovered Fuels (SRF) – A Sustainable

33

Option for Spain”. Madrid, 2009.