4.3 Description of Proposed Building - Devon · Figures 4.3 and 4.4 illustrate colour side and end...

Viridor Waste Management Exeter Energy from Waste Facility

RPS Planning & Development 10 March 2007

4.3 Description of Proposed Building

4.3.1 The proposed scheme is a steel-framed, single storey plant, with integral four-storey office

block. Figures 4.3 and 4.4 illustrate colour side and end elevations of the buildings. A summary

of the building dimensions is provided in Table 4.1.

4.3.2 The total floor area of the building itself is 3513 m² ( 37813ft2), encompassing turbine hall,

waste reception hall, waste bunker, boiler hall, workshop and offices – this is around 30% of

the total site area. The majority of this is used for the delivery and combustion of waste,

recovery of heat, generation of electricity and collection of residues - with delivery bays for

five lorries at the south-end, and collection for 1 lorry to the north.

4.3.3 The layout of the EfW Plant has been designed to satisfy the needs of the intended occupier,

and is based on a standard layout used in other, similar plants. It is intended to spread the

traffic flow around the building, allowing access to all vital areas for collection and delivery for

ease of access and operation. The design responds to the physical constraints of the site,

including the available access points and topography.

4.3.4 The design of the building is intended to add to the surroundings, as the inevitable scale of

such a plant must not simply envelop the neighbouring building forms. The curved roof form

helps to break up the structure’s mass, while maintaining a clean and pure aesthetic. Areas

of space around the entire building, occupying just 30% of the site, reduce the apparent scale

of the design. Consultations have been held with the local planning authorities regarding the

building design and the importance of a building with a strong architectural design as a

opposed to a more industrial design was agreed as part of these discussions.

4.3.5 The building can be seen above the other industrial units among which it sits, yet retains the

height of the existing structure, with a maximum roof-height of around 27.5m (the chimney

stack will be 65m tall). Offices over 4 floors provide 540m2 of space and have 4m floor-to-

floor height, giving ample space to occupants. These offices will facilitate presentations to

school children and others at what will eventually be regarded as a significant educational

service. Remaining areas of the building are designed and built to suit the machinery within.

The boiler hall and waste bunker require the most internal clearance, and are therefore in the

two parts of the building with the greatest floor to ceiling height. Both of these areas have

been designed specifically for their intended purpose, helping to keep the external envelope

as non-imposing as possible.

Table 4.1: Building Dimensions for the Main Areas of the Plant.



External Dimensions Component

Length (m)

Width (m)

Height* (m)

Floor Area (m2)

Main Process Building (housing the oscillating kiln, flue gas treatment plant and residues handling equipment)

53 24 27.5 1272

Turbine Hall, workshop and electrical switch gear room 45 6 27.5 270

Waste Reception Hall 10 36 20 360

Waste Bunker Area 9 24 27.5 216

Ash handling area 40 6 14 240

Office Area 16.75 8 27.5** 135***

Reagent delivery and residue storage area 32 6 27.5 192 * Building heights refer to the highest point ** The offices are within the bunker building and therefore the external height is dictated by the

bunker requirements. The internal height of the offices section is 16m. *** Area per floor, there are 4 floors in total **** The balance of the total floor area is comprised of mezanine floors within the main process

building, waste reception hall and turbine hall .

4.3.6 External doors and windows have been organised so that they relate to their respective

façade, with simple lines and ordered form. Each aspect of the building is expressed through

external use of colour, helping to express administrative areas and separate them from

industrial zones. The Pegasus green (Colourcoat Celestia) used on the upper parts of the

building divide the turbine and boiler halls from the offices and workshop (in grey). The

microrib cladding system is a steel panel sandwich, with expanded foam insulation within –

helping to weatherproof the building, while adding fire protection and thermal insulation.

4.4 Receiving and Handling of Waste

Waste Accepted

4.4.1 The plant can process almost any type of combustible solid waste without pre-treatment. All

wastes burnt within the EfW facility will be non-hazardous, hazardous wastes will not be

accepted. Very strict limits will be applied under the Pollution Prevention and Control (PPC)

Regulations, to the type of waste that can be accepted which will be mixed municipal waste or

waste with similar characteristics to mixed municipal waste.



Traffic Flow around the Site

4.4.2 Flows of the various types of traffic associated with the facility are presented in Figures 4.5 to

4.8.

4.4.3 All vehicles delivering waste, process reagents or removing process residues must weigh in

and weigh out and enter the site via the first entrance. There is an inbound and outbound

weighbridge for this purpose and the traffic flows described below take this into account.

4.4.4 Waste delivery vehicles will normally be 2 and 3 axle rigid Refuse Collection Vehicles

(RCVs). The signage and white lining on the site road will direct the vehicles to the rear of the

plant to where the weighbridge is situated. The weighbridge is positioned such that there is

room for about 20 RCVs queuing between the weighbridge and the public highway, if the

need should arise. However, it would be unusual for more than three vehicles to be queuing

for the weighbridge.

4.4.5 The RCVs would leave the weighbridge and drive onto the turning apron in front of the plant.

The RCV would reverse into one of the four waste tipping bays and then drive out forward

when tipped. Turning immediately, the RCV would drive onto the outbound weighbridge

before exiting site onto Grace Road South.

4.4.6 The signage and white lining on the site road will direct the vehicles collecting ash (four axle

rigid) and scrap (articulated trailers) around the back of the plant to where the weighbridge is

situated. They will leave the weighbridge and drive onto the turning apron in front of the

plant. The vehicle would reverse into bay five for loading and then drive out forward when

full. Turning immediately, the vehicle would drive onto the outbound weighbridge before

exiting site onto Grace Road South.

4.4.7 Vehicles delivering lime - the reagent for the flue gas treatment (FGT) - will be articulated

tankers. The residue from the FGT stage will be collected in vacuum trucks providing a fully

enclosed system for transfer of the material from the storage silo. The signage and white

lining on the site road will direct the vehicles around the back of the plant to where the

weighbridge is situated.

4.4.8 They will leave the weighbridge and drive onto the turning apron going across it and

bypassing the outbound weighbridge exit onto Grace Road South. They will then re-enter the

site and drive into the lime/residue bay at the end of the plant. Once the loading operation

was complete the tanker would drive around the back of the plant, past the inbound



weighbridge, across the front of the tipping hall and onto the outbound weighbridge before

exiting site onto Grace Road South.

4.4.9 Staff cars and visitors will enter the site and turn right immediately into the carpark and will

leave by the same route. Thirty spaces are provided including two for disabled drivers. The

eight spaces nearest the building can be used as a coach park for school visits.

Waste Storage Bunker

4.4.10 The waste is delivered into the reception hall by the RCVs reversing through roller shutter

doors and up to a concrete kerb and emptying into the waste storage bunker. This operation

takes place inside and is therefore protected from the weather and scavangers. The delivery

and storage of the waste within a building prevents wind pick-up of waste and combined with

a high standard of housekeeping will prevent litter escaping from the facility. Figure 4.9 is an

image of a typical waste reception area.

4.4.11 The waste bunker is a concrete structure (about 24m long, 9m wide and 7m deep) that will

hold sufficient waste to keep the process running during night time and week-ends when no

waste is being delivered. Typical storage capacity would be 1% of annual throughput with

additional stacking of waste giving a further 1% under exceptional circumstances. This would

provide up to 5 days operation without delivery.

4.4.12 In the event of the storage capacity being unavailable or too small to cope with shutdowns,

then RCVs would be diverted either directly to a suitably licensed landfill site or to a transfer

station.

4.4.13 The waste reception hall is kept closed by the roller shutter doors. Air is also pulled out of the

hall by the primary air fan and fed into the combustion process. This prevents odours

escaping from the building.

Weighbridge

4.4.14 The operational method for the weighing process is computer controlled and can be easily

modified to suit the needs of the operator, however, here follows a typical description of how

the weighbridge could be operated. Figure 4.10 is an image of a typical weighbridge.

4.4.15 On entering, the RCVs will stop on the inbound weighbridge and weigh, then go and tip out

their load and on leaving, drive on to the outbound weighbridge and weigh again. Each RCV

has a card or tag number that automatically registers the RCV on each weighbridge and



allows the central computer to calculate the waste delivered. The outbound weighbridge has

a ticket printer so the driver has a record of the weights.

4.4.16 The control room is notified of the arrival of the lorry by an intercom situated at the inbound

weighbridge. The plant operator, who can see the weighbridge via CCTV, directs the driver

to the correct tipping bay and opens the correct reception hall door. If for some reason the

RCV does not have a card or tag, or if the operator wants to check a weight, he can see the

records live on the control room monitor and intervene manually. If the lorry is not from a

known bona fide source the driver will be refused permission to tip waste and asked to park to

obtain permission, or to leave site.

Overhead Crane

4.4.17 The waste is handled in the bunker by an overhead grab crane operated from the control

room. The control room overlooks the bunker and has a direct view from a window down the

length of the waste bunker. The crane operator has to feed the plant, mix the waste in the

bunker, keep the tipping areas clear for deliveries during the day and check the bunker for the

presence of unacceptable waste which can then be removed from the pit.

4.4.18 To feed the plant the operator takes a grab full of waste and then puts the crane in semi-

automatic mode. The crane then automatically takes the grab full of waste and positions it

over the waste feed hopper at the back of the bunker. When in position the operator returns

the crane to manual and releases the waste into the feed hopper.

4.5 Combustion of Waste

Waste Feed Equipment

4.5.1 The waste from the bunker is fed into the feed hopper fitted at high level behind the bunker.

This is a square steel cone that directs the waste to slide down into a rectangular feed chute.

This almost vertical feed chute, about 5m long, directs the waste to slide down to the waste

feed ram. Figure 4.11 is an image of a typical waste feed area.

4.5.2 The waste feed chute is kept full when operational, this ensures there is always waste

available to feed into the oscillating combustion cell and provides an air seal. Part way down

the chute is a hydraulically operated guillotine door that can slide shut if the operator wants to

stop waste feeding. Also in the chute is a level switch, which provides an alarm to the

operator if the waste level in the chute is getting low.



4.5.3 At the bottom of the waste feed chute is the waste feed mechanism. This consists of a

hydraulically driven pusher with a refractory lining on the front face to protect against heat

from the kiln. The ram normally sits in the forward position and blocks the bottom of the waste

feed chute, thus protecting any waste in the chute from the heat of the kiln.

4.5.4 When the kiln requires waste to be fed, the ram draws the pusher back past the bottom of the

chute and waste falls down in front of the pusher. The pusher moves forward forcing a plug of

waste into the kiln. There is about 600 kg of waste per push and about 10 to 12 pushes per

hour are needed to keep the kiln fed.

Oscillating Combustion Cell

4.5.5 The oscillating combustion cell is where the waste burns under controlled combustion

conditions. It is completely enclosed and sealed so there can be no fugitive emissions of

smoke or dust. The point of injection and quantity of combustion air are automatically

controlled to provide efficient combustion conditions and to achieve a high carbon burn out,

meeting the WID requirement of Less than 3% total organic carbon in the bottom ash.

Figures 4.12 is a longitudinal section of a complete combustor and Figure 4.13 is a cross

section of the combustion cell.

4.5.6 Municipal Solid Waste (MSW) is a very variable fuel for a combustion process and contains a

variety of sizes and shapes of materials, not all of which is combustible. The oscillating kiln

rocks slowly backwards and forwards on its longitudinal axis and this motion causes the

waste inside the kiln to roll around and break up. This constantly provides fresh material at

the surface for combustion and ensures a very efficient burn.

4.5.7 Waste is fed in at one end and the rocking motion of the kiln causes it to gradually move

down the length, by the time the waste has reached the end of the kiln it is completely burnt

out leaving only an inert mix of ash and clinker.

4.5.8 The cell itself is made up of a twin skin of steel plate rolled into a cylinder (typically 4m

diameter and 15m long). Between the skins are channels for combustion air, which both pre-

heats the combustion air and helps cool the steel skin. The complete combustion cell is lined

with cast refractory for thermal protection.

4.5.9 The complete cell is rotated on external rollers, one set at the front and one at the rear. An

additional thrust roller is included to maintain the lateral position. An external gear drive

provides the oscillation motion by engaging on a toothed ring on the outside of the cell..



Post Combustion Chamber

4.5.10 The combustion cell passes through the post combustion chamber (PCC) (see figure 4.14).

Combustion gases exit the combustion cell through an opening that is itself enclosed within

the PCC. While the main combustion of the solid parts of the waste take place in the

combustion cell, a proportion of fine particles and volatile compounds pass out from the cell

and combust fully in the PCC.

4.5.11 The PCC is constructed from plate steel and is fully refractory lined. At the base of the PCC

are hoppers that allow any dust to fall out of the gas. At the top of the PCC is the connection

to the boiler.

4.5.12 The PCC ensures that the flue gases from the combustion cell have a two second residence

time at above 850°C. This is a requirement from the Waste Incineration Directive (WID).

Clinker Exhaust Hood

4.5.13 Situated at the end of the combustion cell (opposite to the waste feed) is the ash hood. This

allows the ash and clinker to fall out of the end of the cell and into a water bath to quench the

hot material. The water bath also serves as an air seal.

4.5.14 The hood and the water bath ensure no dust or steam escape while allowing the ash and

clinker to get out. A similar water bath (but smaller) exists under the PCC where the dust

settles out.

Hydraulic Power Unit

4.5.15 The combustion cell drive (for the oscillations) and the waste feed ram are driven by hydraulic

power provided from a self contained hydraulic oil unit.

4.6 Combustion Auxiliaries

Start-up and Temperature Back-up Burners

4.6.1 The plant is provided with two gas fired burners which will also be capable of burning oil,

although it is intended to operate on natural gas. The primary burner which sits at the end of

the combustion cell is only used when starting-up the plant to create conditions within the

combustion cell suitable for the ignition of waste and to supplement the secondary burner in

maintaining 850°C until the process is self sustaining.



4.6.2 The secondary burner is mounted in the top part of the PCC and is used to preheat the PCC

and boiler plant during start-up and to maintain the temperature in the PCC above 850

centigrade at all times whilst waste is being fed to the combustion cell. Other than on start-up

this burner would only be used occasionally in case of poor quality combustion. This burner

is required by the WID.

4.6.3 Under normal operation the Secondary burner would only fire for one or two percent of the

plant operating time.

Primary Air Fan

4.6.4 A centrifugal fan supplies the flow of primary combustion air. This air passes through a

rotating joint on the combustion cell and provides air underneath the burning waste. This is

done through a series of nozzles in the refractory lining. The amount of primary air is

controlled automatically to provide the best combustion conditions.

4.6.5 Primary air is drawn out of the waste reception hall via a duct and as detailed previously

prevents odours from the waste reception hall escaping.

Secondary Air Fan

4.6.6 The secondary air is injected into the combustion cell above the waste. It is used to control

the temperature of combustion gases. It also provides oxygen to allow final combustion to

take place in the PCC. The amount of secondary air is controlled automatically to provide the

best combustion conditions.

4.7 Energy Recovery

Steam Boiler

4.7.1 The heat recovery from the hot combustion gasses takes place in the boiler. This is

connected directly to the PCC.

4.7.2 The boiler will have a single drum and natural circulation. It will be of horizontal arrangement

and sit at the side of the combustion cell.

4.7.3 The boiler is made up of a number of sections comprising:

• Two empty passes with water tube walls. Water in these tubes is being heated

predominantly by radiation.



• A horizontal section containing evaporators and superheater tube bundles where water

and steam respectively are heated predominantly by convection. These tubes are

mounted within water tube walls.

• A final horizontal section containing economiser tube bundles within a plain metal casing

heating water by convection.

4.7.4 The tube bundles are kept clean by rapping gear fixed to the side of the boiler. This

mechanism works on a timed basis and uses mechanical hammers to vibrate the dust off the

tubes.

4.7.5 The boiler is insulated and clad to reduce heat loss and to prevent the risk of personnel

contact with hot surfaces.

External Economiser

4.7.6 An additional external heat exchanger will be fitted to recover further energy from the flue

gas. This will be fitted either at the inlet or outlet to the Flue Gas Treatment filter and will

recover low grade heat in a hot water circuit. This will be used to reheat boiler feed water.

Boiler Feed Water Treatment

4.7.7 The boiler water has to be treated before going into the boiler. Mains water is first passed

through a deionisation unit to prevent scale build-up in the boiler. The water is then dosed

with three chemicals; a neutralising agent, an oxygen scavenger and a phosphate treatment -

these prevent internal corrosion and the build-up of deposits.

Turbine Generator Set (heat and electricity option)

4.7.8 Figure 4.15 is an image of a typical turbine. The turbine-generator set converts the high

pressure steam into electricity by passing the steam through a series of turbine blades

attached to a central shaft. This shaft is then attached to a generator that produces electricity.

4.7.9 Typical conditions would be:

Turbine inlet 35 bar and 360°C.

Turbine outlet : 900 mbar vacuum and 45°C.



Turbine By-pass

4.7.10 There may be occasions when the plant has to run but the turbine cannot, e.g. turbine

maintenance. The turbine bypass duct allows this by sending steam directly to the Air Cooled

Condenser (ACC).

Air Cooled Condenser

4.7.11 The purpose of the condenser is to condense the steam by dissipating low grade heat to the

atmosphere. This is situated at the rear of the plant. The condensate recovered is returned to

the boiler for re-heating.

Connecting Pipework

4.7.12 Standard steel piping connects all the elements described above. The type of flanges and

fittings depends on the pressure and the temperature as well as the thickness of the pipes.

Supports depending on alignment; expansion compensators are placed where they are

required, in particular so as not to impose stresses on the pumps or the turbine. All hot

pipework and critical items of equipment are insulated (rock wool and aluminium cladding) for

the purposes of both personnel protection and energy conservation.

4.8 Flue Gas Treatment and Exhaust

4.8.1 Flue gas treatment (FGT) is needed to ensure dust, acid gases dioxins/furans and heavy

metals are removed from the flue gas and the emissions from the stack comply with WID.

Many different technologies exist to provide this treatment and the selection of the technology

depends upon the individual economic and space constraints for the plant in question. The

final selection is done in conjunction with the PPC application.

4.8.2 A typical system for the control of acid gases is described here, known as a dry system.

Semi-dry and wet systems may also be considered, however their performance with respect

to the environment must essentially be the same to comply with the WID. The dry system will

employ hydrated lime or bicarbonate to neutralise the acid gases.

4.8.3 Activated carbon injection is used for the control of dioxins/furans and mercury, acting to

absorb these pollutants from the flue gas and retain within the fine matrix of cavities in the

activated carbon powder.

4.8.4 There is also a requirement to provide control of Oxides of Nitrogen (NOx), these are known

as DeNOx systems and they also fall into two main categories, Selective Non-Catalytic



Reduction (SNCR) systems and Selective Catalytic Reduction (SCR) systems. It is proposed

to use SNCR within the development. This system chemically reduces the NOx to nitrogen

and water through the injection of a reducing reagent. Reducing agents typically employed in

SNCR systems are ammonia and urea; it is proposed to use urea within the development.

Reagents Storage, Preparation, Extraction and Injection

4.8.5 The system for handling the reagents consists of:

• a silo for storing hydrated lime (or bicarbonate) with pneumatic unloading of the delivery

tanker transportation vehicles and extraction and dosing system

• a small silo for storing the active carbon (either from tanker or big-bags) emptying station

and extraction and dosing system

• a storage area for urea bags, a solution preparation tank

4.8.6 Powdered hydrated lime (or bicarbonate) and powdered activated carbon are injected into the

flue gas duct after the boiler.

4.8.7 Urea granules (typically used as a fertiliser on agricultural land) are used as a reagent to

remove NOx. They are mixed with water first and then sprayed as a solution into the post

combustion chamber.

Bag Filter(s)

4.8.8 Following injection of the reagents, the flue gas passes through a filter. This consists of a

large number of long sock type filterbags (typically 600) in a metal casing. Excess reagent,

the salts of acid gas neutralisation, activated carbon powder and any dust particles collect on

the outside of the filters while the clean gas passes through. At regular intervals a pulse of

compressed air is used to knock off the dust build up which falls down into hoppers at the

base of the filter housing.

4.8.9 This dust is removed from the filter base by an enclosed conveyor and conveyed to the

residue storage silo. The complete system is sealed to prevent any dust escape.



Exhaust Fan

4.8.10 A large centrifugal fan sits between the filter and the stack. This pulls the flue gases through

the system and ensures a slight vacuum at all times to prevent dust escape from the

upstream, combustion cell, post combustion chamber, boiler and flue gas treatment plant.

Stack

4.8.11 A free standing steel stack of typically 65m will be provided.

4.9 Residues

Combustor

4.9.1 Ash and clinker from the PCC and combustion chamber fall into separate water baths where

they are quenched (typically from 500°C down to ambient). Each water bath contains a chain

scraper conveyor that continuously removes the cooled ash and clinker. As the conveyor

rises out of the water, the water drains back into the bath and the ash and clinker are

transported to an ash treatment area.

4.9.2 The ash is deposited directly into an ash/clinker concrete bunker. The clinker passes along a

series of vibrating conveyors, and magnets. Large reject items are removed first by the

operator (infrequently), then ferrous metals are removed and finally clinker is deposited into

the ash/clinker bunker. The scrap metal is deposited in a separate concrete bunker. Reject

items are manually handled into a skip for disposal as appropriate (they may be suitable for

scrap metal).

4.9.3 The ash/clinker and scrap are stored in two separate concrete bunkers, approximately 100

cubic meters capacity each. An overhead crane runs above both bunkers and can take

ash/clinker or scrap to be loaded into a wagon parked in the end bay of the waste reception

hall. For loading ash/clinker the crane has a clam type bucket and for scrap a magnetic

attachment.

4.9.4 The loading operation takes place entirely within the building so that noise and dust are

contained.

Boiler and Flue Gas Treatment (FGT) Residues



4.9.5 At the bottom of the boiler there are several places where deposited ash is extracted. This

ash is extracted in a sealed conveyor system that then joins the FGT residue conveyor before

being added to the residue silo.

4.9.6 The residue silo is a closed steel design with a cone at its base. Beneath the cone, a loading

system is fitted to load the residue directly into a sealed road tanker for onward transport to a

suitably licensed treatment facility.

4.10 Water Systems

Mains Water

4.10.1 The plant will be connected to the mains water system. Mains water will be used for the

following:

• domestic usage for the staff on site;

• feeding the demineralised water system in turn used to feed the boiler water treatment

plant and urea mixing plant; and

• standby facility for the rainwater system during dry periods.

Rain water Harvesting

4.10.2 Clean rainwater run-off from the building roofs will drain into a clean water recovery system.

All these clean water flows will be routed to a sump and then the water pumped to a clean

process water storage tank in the main building.

4.10.3 This tank will then feed the following water systems:

• top up of the process water system;

• cooling water for the boiler blow down system

• top up the elevated fire water tank: and

• wash-down water for hosepipes.

4.10.4 If no rain water is available (during dry periods), the system will be topped-up by mains water.

Dirty water Recycling



4.10.5 Water overflow from the Combustor and PCC ash baths has a high level of suspended solids,

these are the finer particles of ash. This water overflows into the floor drains where wash-

down water and boiler blow-down water mix together. The floor drains all fall back to a sump

where the water is pumped into a recycling system.

4.10.6 The water first goes through a plate separator where the majority of solids are removed by

settling. After this two dirty process water settling/storage tanks will hold the water until it is

re-circulated to the ash baths.

4.10.7 The ash baths are net users of water, firstly water evaporates as hot ash is quenched. This

evaporated water goes into the combustion cell and mixes with the flue gases. Secondly the

ash recovered by the conveyor retains about 20% water by weight, even after draining. Thus

the dirty water system looses water to the process and needs topping up from the rainwater

harvesting system.

4.11 Process Regulation and Control

General

4.11.1 The plant is controlled through a Programmable Logic Controller (PLC) with all aspects

automated. The operator interfaces with the PLC through a Supervisory Control and Data

Acquisition (SCADA) system displayed on the control room monitors. Aspects of safe

operation, start-up and shut-down are dealt with by the PLC.

4.11.2 The control room overlooks the waste reception hall so that the operator can see the waste

being delivered, operate the grab crane and monitor the plant SCADA from the same location.

4.11.3 A CCTV system allows the operator in the control room to see other areas of the plant.

Typically these would be:

• A combustion cell observation camera installed on the end wall of the ash hood, to see

the combustion conditions.

• An observation camera for the waste feed hopper

• Inbound and outbound weighbridges

• The entrance and exit of the site

• The ash and scrap sorting and loading area

Emissions Monitoring



4.11.4 A dedicated emissions monitoring system is installed. This takes continuous samples from

the stack and analyses for a range of substances dictated by the Environment Agency.

4.11.5 The selection and operation of this equipment is dealt with as part of the PPC permit.

Data Collection

4.11.6 Data collection and analysis is an important part of plant operations to ensure the plant is

performing at its most efficient. Data is collected on a continuous basis from a number of

resources and is stored on the plant SCADA system. Analysis of the data would normally be

carried out on a monthly basis but as the information is collected on an almost continuous

basis, any time period can be analysed.

4.12 Miscellaneous Equipment

Fuel-oil Tank

4.12.1 The auxiliary heat required predominantly for plant start-up will be fuelled using natural gas.

Hence there is no requirements for site storage of light/ heavy fuel oils.

Compressed Air

4.12.2 A compressed air circuit will provide air for actuated valves on the plant and air tools etc.

Walkways, Platforms, Stairs and Ladders

4.12.3 A series of stair towers, walkways and platforms allows operators to get around the plant to

make routine cleaning, observation and maintenance.

4.13 Flood Protection

4.13.1 A number of features have been integrated into the plant design to prevent or minimise

pollution as a consequence of flooding of the Marsh Barton Estate (see Chapter 10). It is

noted that a warning would be received within which time it would be possible to stop burning

waste and shutdown the plant to a safe condition.

4.13.2 Within this period:

• a temporary barrier would be erected across the open face of the waste bunker to

prevent pollution by waste flotation;



• bunded tanks would be checked for residue and emptied as appropriate, the drains would

be washed down of residue, the floor drains sump will be emptied and isolated from the

process hall floor to prevent pollution by inundation with flood water; and

• FGT residues within floor mounted conveyors would be isolated from feed sources and

run to evacuate residues from within and thus minimise pollution by inundation with

floodwater.

4.13.3 Additionally the following passive features have been integrated to prevent inundation by

water and consequent pollution;

• bottom ash and ferrous scrap are stored within concrete bunkers with 4m walls and one

way drain valves;

• rejected ash and ferrous scrap residues are stored within a skip with 2 meter high sides

secured to the floor;

• flue gas treatment reagents (lime and PAC) are stored in closed silos 6 meters above

ground level;

• flue gas treatment residues are stored in a closed steel silo mounted 6 meters above

ground level; and

• demin water chemicals (HCl - acid and NaOH – caustic) and boiler water treatment

chemicals are stored in sealed and bunded tanks secured to the floor to prevent

discharge of contents through flotation and rupture of connecting pipework.

4.14 Energy Utilisation

Process

4.14.1 By its very nature the incineration of fuel, in this case household waste, produces energy in

the form of heat. This heat is the product of the underlying combustion process and

materialises in the form of hot exhaust gases. In order to usefully utilise this energy it is

common practice to firstly produce high pressure steam in a boiler. This then allows both the

production of electrical power as well as a useful transmission medium for the heat energy.

4.14.2 The standard boiler arrangement produces steam at 36 bars and 360°C. (this steam having

approximately 115°C of superheat) which are high enough conditions to enable an efficient

conversion to mechanical power in a steam turbine.



4.14.3 The process being proposed is based on a fuel or waste input of 50,000 to 60,000 tonnes per

annum. Using this requirement, this application has been based on a thermal process design

capable of continuously handling 16.3MW of potential energy input. (As it will be necessary to

burn supplementary fuel at process start up / shut down and to occasionally maintain the

process temperature when the waste is of poor quality, some auxiliary fuel will have to be

burned. The overall waste input is therefore of the order of 16MW).

4.14.4 From this heat input it is possible to retrieve approximately 12.25MW in the form of high

pressure steam with a further 0.8MW available in the form of hot water recovered from the

flue gas treatment system downstream of the boiler. This approximately 13MW of heat is

useful for export either by conversion to electricity or as heat. For the purposes of clarity,

additional pipework required to facilitate the export of heat energy beyond the boundary of the

site is not included as part of this application.

4.14.5 The equipment required to operate this process consumes electrical power. In total this

power consumption equates to around 0.57MW electrical (e) and it is beneficial to ensure that

sufficient power is generated by the process to cover this demand as a minimum.

Mechanical /Electrical Energy Production

4.14.7 The process of deriving mechanical power which can subsequently be used to generate

electrical power, requires the steam energy to be expended through a steam turbine. In this

process the steam loses both pressure and temperature as it expands through, and turns the

blades of, the turbine. This expansion process is influenced by both the upstream (i.e. boiler)

and the downstream (i.e. condenser) steam conditions. However, as marginal changes in the

low pressure conditions affect the volume of the steam far more, it is the downstream

conditions that affect the overall performance and mechanical efficiency the most.

4.14.8 The steam exhausting from the turbine must be condensed back to water prior to re-entry to

the boiler to complete the cycle.

4.14.9 As the bulk of the energy contained in the steam is in the form of latent heat (the energy

required to change from the water phase to the steam phase) a large amount of energy is

released in this condensation process. The temperature of the heat released is related to the

exhaust pressure – i.e. as the exhaust pressure is lowered (thus increasing the mechanical

power) the temperature of the heat energy released will drop. Alternatively as the temperature

of this energy increases there will be a subsequent (and significant) drop in the electrical

generation potential but an improvement in the grade or temperature of the heat released

(greater potential for use in heating schemes).



Heat Energy

4.14.10 Heat energy can be exported in a number of different ways depending on the requirement of

the end user.

4.14.11 In the case of high/medium pressure steam, steam could be derived either as live steam

directly from the boiler (at boiler exit conditions) or by extraction from the turbine at dedicated

bleed points part way along the casing at lower pressures and temperatures.

4.14.12 Steam extracted from the boiler will not pass through the turbine and hence will not produce

any mechanical/electrical power. Steam extracted from part way along the turbine will

produce some mechanical power and can therefore also contribute to the overall electrical

export potential of the system. Again the relationship boils down to that of

temperature/pressure – the lower the pressure / temperature of the steam at the bleed point

the more mechanical (hence electrical) power that can be realised from it. However, there will

be less energy in the bleed steam.

4.14.13 When exporting steam from the process it is necessary to replenish the lost water from the

system. As the boiler water needs to be treated, to do this continuously is both costly and

wasteful. Therefore, a normal design objective would be to retrieve the condensate from the

external process and return it to the boiler. If the nature of the external process prevents this

because of contamination or other issue it may be necessary to generate steam locally at the

customer’s site using higher temperature steam from the main process. This can be done in a

steam raising heat exchanger.

Medium or Low Pressure Hot Water

4.14.14 Heat can also be exported in the form of hot water. This is more usual when the energy is

required for background or space heating of buildings for instance. However, in some cases

high pressure hot water schemes can transfer heat for use in processes at temperatures well

in excess of 100°C.

4.14.15 In the majority of systems it would be normal to export the heat in an auxiliary system

separate from the main boiler steam system by using heat exchangers to transfer heat from

the steam into the secondary water circuit. Again the same relationship exists between

mechanical/electrical energy and the temperature of the heat energy.

Marsh Barton Proposal

4.14.16 Whilst the facility offers considerable scope for the export of both heat and electrical energy,

detailed consideration has been given to two possible schemes at Marsh Barton:



• the export of steam to local industry; or

• the export of heat via a low temperature hot water district heating system to various

discrete buildings both on the east bank of the River Exe and in the Marsh Barton estate

itself.

In both these cases the additional pipework required to transport the heat energy to the

customer(s) is not included within the scope of this planning application.

4.14.17 Several potential industrial heat customers have been identified within the Marsh Barton

estate, all of which are accessible by the heat supply network’ (subject to a separate planning

application)

Steam Export to Industrial Customer

4.14.17 A potential industrial customer has been identified who has a site about 600m from the

proposed location of the EfW site

District Heating Scheme

4.14.18 The location of the site has considerable potential for the export of heat in the form of a low

temperature, hot water, district heating scheme. Pipe routes have been assessed which

would enable heat to be provided to the districts of St Leonard’s & St Loye’s and possible

buildings in the St Thomas’s areas of Exeter.

4.15 Demolition of the Existing Incinerator

4.15.1 The development is proposed on the site of the former (circa 1996) Exeter incinerator, which

has been partially demolished whilst the remaining buildings and facilities are being utilised

by Devon Waste Management and Coastal Waste as a waste transfer station for residual

municipal and recyclable wastes. The site is currently occupied by:

• the redundant incinerator and ancillary equipment (excluding the stack and flue gas

treatment plant which have already been removed);

• the old incinerator buildings;

• areas of hardstanding;

• ancillary machinery and accommodation;



• waste transfer station facilities;

• an electrical substation; and

• underground site drains.

4.15.2 The original building drawings have been reviewed and a site visit undertaken to identify the

extent of the current site structures and determine whether reuse of part or all of these

facilities would be possible.

4.15.3 The existing incinerator, associated equipment and incinerator buildings are not

suitable for reuse within a modern EfW facility and will be demolished and materials either

disposed of, recycled or salvaged for use elsewhere dependant on economic values

4.15.4 It is proposed that a review of the existing piles be undertaken and piles reused where their

location and and design is found to be acceptable

4.15.5 It is proposed that the existing concrete hardstanding will be broken up and reused as

aggregate on the current site or elsewhere depending on economic and practical

circumstances

4.15.6 Hazardous materials including asbestos, galbestos, PCB’s and zonotic spores are known to

be present within the existing buildings and equipment. These will be removed from site in

accordance with relevant legislation and best practice guidance and disposed of to suitable

facilities.

4.15.7 It is planned that before demolition of the existing facility commences, the existing transfer

station activities will be relocated elsewhere It is estimated that the demolition process will

take place over a 6 month period.

4.15.8 Demolition procedures will be in place to ensure that activites are performed in such a

manner as to minimise the release of dust to the atmosphere and that works are carried out

in accordance with relavant legislation and best practice guidance.

4.15.9 For a more detailed description of the demolition phase, refer to the appropriate section

within chapter 4 (Description of Development) of the accompanying EIA



Drainage Facilities

4.15.10 The site is served by both foul sewers and clean surface water drainage systems with

underground sealed tanks and interceptors presumed. The proposed development will

integrate a new system of foul sewer and surface (clean) water drainage, however the current

systems should be retained until the risk of contamination by the products of demolition are

mitigated, the connections to the system may then be capped and the underground structures

removed.

4.16 Development Programme

4.16.1 The following sets out the likely timescales for development.

Table: Stages of Development

Stage Activity Duration

Prepare site 1 Move existing operation to another site. 6 months

Prepare site 2 Demolish old structures and level site 6 months

Pre-engineering Design and procurement. 9 months

Groundworks Pile site, construct waste bunker and lay main concrete slabs. Install buried services.

9 months

Main construction Erect main building, install equipment and services. 18 months

Commissioning Testing and start-up of the plant. 6 months

Construction Phase Working Hours

4.16.2 Activity levels would fluctuate during the course of the construction programme. Generally,

the construction activities would be expected to be carried out between 07.00 – 19.00hrs

Monday to Friday and 07.00 – 16.00hrs on Saturdays. Normally work hours on a Saturday

would be limited to 07.00 to 13.00 however at certain times during the construction phase it

would be beneficial for smaller groups of contractors to work until 16.00 to avoid many trades

working in close proximity to one another and hence ease safety considerations. Noisy

activities such as piling would not take place on a Saturday afternoon.

4.16.3 Certain works may have to be undertaken during the evening or at night. If that were the case

then prior agreement would be sought. Working on Sundays would be subject to reasonable

notice and for temporary periods.



4.16.4 Commissioning work (and subsequent plant operation) will be on a 24 hour, 7 days per week

basis. However most of the commissioning work takes place inside.

Access and Traffic

4.16.5 The construction phase would generate traffic in the form of deliveries to site by HGVs and

also construction workers in cars and vans. It is not expected that any significant amount of

material would leave site during construction. Construction workers would need to park their

cars off site.

4.16.6 The Traffic Impact Assessment chapter in the EIA deals with construction traffic and parking

plans in detail.

4.16.7 Deliveries of parts and material will be directly to site as they are needed. No large scale

storage of materials or equipment would be needed on site.

4.16.8 Access to the site will be via the Marsh Barton Trading estate road from the B3123.

4.16.9 It is not envisaged that there will be any requirement for road closures during construction. It

may be that during certain periods there is slight disruption to Grace Road South due to utility

companies putting in new connections.

4.17 Utilities and Infrastructure

Existing Utilities

4.17.1 A desk top study has determined existing utilities that may be affected by the development. It

can be determined from this that the following will be of particular note:

• Relocate the existing 11 kV Western Power substation (and associated underground

cables) from it’s current location in the centre of the site, to a location on the eastern edge

of the site immediately adjacent to Grace Road South. This will need to be carried out

before any significant demolition work is carried out. This work needs to be carried out by

Western Power or its subcontractors.

• Removal of the redundant 33kV buried cable on the western edge of the site. This work

needs to be carried out by Western Power or it’s subcontractors.

• Agree safe working practices for demolition and construction work in close proximity to

the 132 kV overhead power lines that run down the eastern edge of the site. This must

include for the use of mobile cranes. The advice of Western Power should be taken into

account and any line diversions required should be agreed well in advance.



• Agree safe working practices for demolition and construction work in close proximity to

the railway track running immediately adjacent to the site to the east. This must include

for the use of mobile cranes. The advice of Newtwork Rail should be taken into account

and any special safety measures required should be agreed well in advance.

New Connection Requirements

Electrical Connection for Import and Export

4.17.2 The development requires electrical power, initially for construction and subsequently for

operation of the facility.

4.17.3 The facility includes a turbine generator set driven by steam from a heat recovery boiler.

Under normal operation the facility would generate all its own power requirements and have

capacity to export electricity to the local network. However during shutdown and start-up, the

facility relies on connection to the local distribution system to import electrical power.

4.17.4 The local 11 kV distribution system, operated by Western Power, is a buried cable in Grace

Road South. Western Power have confirmed that this system would be capable of accepting

exported power as well as providing power to site, without any reinforcement work. However

the existing 11 kV supply to site would have to be moved to the site frontage where a new

substation would be needed.

4.17.5 An additional short length of buried cable in Grace Road South is recommended by Western

Power to ensure the new substation is part of a ring main rather than a spur – this improves

security of supply.

Table 4.2 provides provisional information on the site electrical requirements.

Table 4.2: Site Electrical Requirements

Plant status Typical import Typical export

Construction 200 kW via temporary step down transformer. None

Start up and shutdowns 600 kW via permanent plant step-down transformers. None

Operational (expected 90% of the time) None 2700 kW for export generated

at 11 kV

Design maximums 1 MVA 3.5 MW

Note MW= Mega Watts



Gas

4.17.6 Natural gas is used for the start-up and support burners. Low pressure gas is required either

directly from a low pressure main or via a let-down station off a medium pressure main.

4.17.7 Wales and West Utilities have confirmed that both low pressure (90 mm pipe) and medium

pressure (315 mm pipe) gas mains are located in Grace Road, within 100 m of the site.

4.17.8 There is a 350mm high pressure gas main to the east of the site and railway line. A

connection to this high pressure gas main would not normally be suitable for this type of

facility.

Water and Drainage

4.17.9 The development will require connections to the potable water main, foul sewer and surface

water sewer.

4.17.10 Potable water will be required for staff welfare facilities on site as well as for topping up

process water requirements (a rain water recovery system will provide some of the process

water needs).

4.17.11 A foul sewer connection will be required for the staff welfare facilities on site. There may also

be an occasional requirement to dispose of treated boiler water via the sewer connection,

although normally this would be re-used on site.

4.17.12 A surface water sewer connection will be required for rain water run-off in excess to that

required by the recovery system on site. It is probable that this would be provided through

the existing site connection and existing site interceptors.

4.17.13 During construction, any temporary site accommodation and welfare facilities would also

require connections to potable water and foul sewer.

4.17.14 South West Water have confirmed the availability of the following services, all running along

the frontage of the site in Grace Road South:

• Potable water ring main

• Foul sewer

• Surface water sewer



Telecommunications

4.17.15 The facility will require normal telephone and internet connections for both operational and

construction phases.

4.17.16 BT Openreach have confirmed the availability of distribution points along the frontage of the

site in Grace Road South.

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