Cost study: Incineration plant

<b>At-a-glance guide
Mersey Valley Processing Centre, Widnes</b>

<b>Project</b>
State-of-the-art sewage incineration plant

<b>Client</b>
United Utilities (formerly North West Water)

<b>Location</b>
Bank of River Mersey at Widnes

<b>Project significance</b>

 

 

• Pioneer of new generation of environment-friendly sewage treatment and incineration plants required by new European legislation
• Design had to reduce impact of bulky industrial plant
• Planning permission granted after public inquiry
• Won two awards for design and implementation

<b>Construction cost</b>

 

 

• Building cost £12m
• Part of £40m civil works contract including treatment plant
• Value engineering reduced costs by 20% pre-tender

<b>Contract</b>
Lump-sum turnkey contract under Institute of Chemical Engineering’s Red Book form of contract

<b>Contract period</b>
22 months, completed November 1998

<b>Client’s brief</b>
EC legislation banning the disposal of sewage sludge at sea from October 1998 forced United Utilities (formerly North West Water) to develop a new sewage-processing strategy covering the entire Mersey basin. The strategy aimed to incinerate some 52% of sewage waste by the year 2000, and to recover energy from the heat produced.
Architect Austin-Smith:Lord was commissioned by the water authority to plan and carry out the concept design for a waste incineration plant at Shell Green in Widnes. Once the site had been chosen and planning permission granted, the scheme was handed over to project manager and engineer Bechtel which, in turn, novated Austin-Smith:Lord as architect and landscape architect.
The project was very innovative for the UK. The client pioneered an experimental de-watering process, while the fluidised bed incineration is a state-of-the-art process that reduces the amount of ash produced. The gas clean-up process is built to German standards, which are far higher than UK standards.

<b>Award-winning industrial project</b>
Despite the complex and groundbreaking nature of the project, it was completed to budget and on time, and both client and designers are pleased with the result. The project has won both an RIBA award and a Construction Industry Award, demonstrating its excellence in design and implementation.
The judges for the Construction Industry Awards said: “This is an outstanding example of how a good team can deliver a major project to a very tight deadline. Early architectural input, value engineering and design for buildability and operational efficiency have produced a high-quality complex constructed with a superb safety record.”

<b>Planning issues</b>
United Utilities appraised more than 80 sites, scoring each one according to set criteria. Shell Green scored the highest of any site, as it already contained the Mersey Valley’s main sewage pipeline and had an established industrial character, thanks to a neighbouring power station.
However, Cheshire County Council’s concerns over emissions from the plant led to a DOE planning inquiry in autumn 1996. Evidence presented at the inquiry included a visual impact assessment taken by the architect from key viewpoints within a 50 km radius of the site. Once the project had been completed, these visualisations were compared with actual views and found to be highly accurate.

<b>Design</b>
The design of the treatment plant involved laying out the elements into an efficient and modular production line, so that the incineration plant could be expanded at later dates. The scheme was also designed to contribute a visually cohesive complex of buildings to the area and create a plant that expressed the industrial processes contained within it. With a maximum height of 30 m and a footprint of 200 × 80 m, the development is impossible to conceal. An all-embracing rectilinear building shell was dismissed as being too bulky. Instead, the two main components of the process – the de-watering plant and the incineration plant – are housed in separate building envelopes linked by a smaller-scale element incorporating odour and process controls. A shallow curved roof closely follows the height and profile of the incineration equipment, and this form is repeated in a complementary way over the de-watering building. From a 30 m high crest, the roof curves down to much lower eaves at the western end, where it appears closer in scale to the existing office buildings and housing beyond.
The variations in roof profile and the articulated block design help to reduce the overall bulk and skyline of the development. In contrast to the predominantly rectilinear industrial buildings in Widnes, this design approach produces a softer building outline and helps its assimilation into the wider landscape of the Mersey valley.
The functional separation of processes in the incinerator building is accentuated visually by the articulation of the roof and walls. This further reduces the apparent building bulk and scale when viewed from a short distance.
A central element housing the electrostatic precipitators is partly roofed over but not enclosed, allowing glimpses of the process and views through the buildings. The recesses in the main roof also provide screened zones for smaller scale external plant and equipment that would otherwise disrupt the clean lines of the roof. The curved roof profile and high level glazing of the incinerator break down the apparent bulk of the building from the surrounding residential and industrial area.
The external elevations are stratified into three horizontal layers, which also helps to reduce the apparent bulk. At upper levels, walls are glazed to give views out into the complex and let in natural light. The walls below are clad in metal-faced composite panels. The base is clad in architectural concrete blockwork with some limited glazing.
Ancillary buildings are treated in a complementary manner. The workshops and substation use gentle curved roofs to echo the form of the principal buildings, and, where appropriate, they use the same palette of external materials – glazing, blockwork and cladding. External tanks and silos are fully or partly clad to form visually integrated local groupings and relate to the general building character.
The construction materials are suitable for a high-quality industrial development, selected for their durability and low maintenance. The colours of the buildings, ancillary structures and silos are within the mid-tone range – silver greys and warm greys – which helps assimilation of the complex into its surroundings.

<b>Procurement</b>
The buildings were let as part of the overall civil works contract for the entire plant. This was let in competitive tender, based on an outline design and performance specification rather than measured quantities, and as a single lump-sum turnkey contract under the Institute of Chemical Engineering’s Red Book form of contract. A generic method of specification based largely on durability of materials was developed by the designers.
The entire site development was made up of three separate contracts: the incinerator/gas clean up system (£23m), de-watering plant and civil works (£40m) and the pipeline contract (£3.5m). The incinerator process contract was let ahead of the civil contract so that the process plant could be sized and configured before the buildings were designed in detail. The de-watering plant was pre-purchased and passed to the civil contractor which subcontracted its installation to the plant manufacturer. Bechtel Engineering managed the overall programme.

<b>Cost commentary</b>
The costs may appear high for a simple shed, but the building was subject to aesthetic treatment of its elevation and profile and allowed for easy expansion of the process plant.
High-quality external finishes were employed with a view to reducing future maintenance costs and as part of the aesthetic treatment.
The elemental costs are for the buildings alone and are extracted from the larger contract for the entire plant placed with Tarmac (now Carillion) as design-and-build contractor.

<b>Specification</b>
Structure

 

 

• Reinforced concrete foundations
• Steel frame with galvanised finish
• Precast concrete floor units
• Industrial steel staircases and intermediate floors

<b>Cladding</b>

 

 

• High-level external cladding in composite metal cladding panels with PVF2 silver finish fixed to steel frame
• Strip windows in mid-grey
• powder-coated aluminium
• Low-level cladding in buff Forticrete architectural blockwork
• Overhead industrial doors in mid-grey prefinished insulated panelling
• Personnel doors in painted solid-core timber
• Louvres in dark-grey polyester powder-coated aluminium

<b>Roofing</b>

 

 

• Standing-seam aluminium roofing with maximum 4 m overhangs and light-grey PVF2 finish
• <b>External elements</b>
• Staircases, walkway in galvanised steel
• Process tanks in stainless steel
• <b>Internal finishes</b>
• Interiors of main process buildings in low-maintenance self-finished materials, including fairface blockwork and concrete, galvanised steel staircases and walkways and sealed concrete floors
• Main control room and visitor facilities have demountable partitions, raised access floors and suspended ceilings