Slough Multifuel Energy-from-Waste: Technical Insulation & Trace Heating
The Result
Powertherm teams installed over 30,000m² of technical insulation and sheet metal cladding fabrications for the Boiler, Turbine and auxiliary systems, and associated equipment, ducting and pipework across 2 lines at Slough Multifuel. As well as 8,906 linear meters of electrical trace heating, including frost protection and temperature maintenance systems, at the energy-from-waste (EfW) power plant, that’s situated in the south of the UK.
Working efficiently and safely, with no RIDDOR reportable health and safety accidents, a site team of over 50 (peak) professionals helped to successfully deliver the plant, which was able to commence operations ahead of schedule.
The Challenge
Our client was entrusted with constructing the new EfW plant that converts solid municipal, domestic and industrial waste, and waste wood, into electrical and thermal energy.
The process begins with waste being burnt in a large furnace, generating intense heat. This heat boils water, producing steam. The pressurised steam is then directed through pipework to a turbine, which, under the force of the pressurised steam on its blade’s, spins, creating mechanical energy. The turbine is connected to a generator that converts this energy into electrical energy. Steam produced during this process is either condensed backdown to water and reused in the initial boiler system or, pumped to local businesses to be used in their processes or, in some cases, utilised in district heating systems.
To minimise environmental impact, the plant uses advanced filters to clean the flue gases, reducing pollution before it is released into the atmosphere via the stack.
Slough Multifuel can produce 60 MW (approx) of electrical power and is expected to divert an estimated 480,000 tonnes (p.a.) of residual waste from landfill, supporting the government’s strategy to reduce landfill usage, waste export and protect the environment. Up to 92MW of thermal power per line will also be produced; the steam produced will continue to be efficiently piped to a neighbouring confectionary plant on the Slough Trading Estate.
(Image Credit: SSE)
Our task was to support the engineering, construction and procurement (EPC) contractor, Hitachi Zosen Inova (HZI) (now known as Kanadevia Inova) to deliver this project by providing them with industrial insulation and electrical trace heating services. These industrial services help ensure the plant runs efficiently through improved heat conservation, process stability, and frost protection. As well as help reduce operating costs, enhance safety, protect equipment lifecycles and contribute towards environmental goals through optimising energy consumption and reducing carbon emissions.
Project / Site Details
Location: Slough, UK
Industry: Power Generation
Type: Energy-from-Waste (EfW)
Fuel: Municipal, commercial and industrial waste and, waste wood
Processing Capacity: 480,000 tonnes
Power Outputs: 60 MW Electricity & 92 MW Thermal
End User: Scottish and Southern Energy (SSE)
What We Delivered
Insulation
Our scope of services included the supply and expert installation of industrial insulation to several systems within Slough Multifuel including, the Boiler, Common Steam Piping, Flue Gas Treatment, Solid Handling, Water-Steam Cycle, and Balance of Plant, as well as associated ductwork and piping.
Boiler / Common Steam Piping (CSP)
Over 15,000m² of mineral wool insulation and sheet metal cladding was installed by Insulation Operatives to various equipment and pipework within the Boiler/ CSP systems, including:
- Boiler & Blowdown Tanks
- Grate – Grate Riddling
- Primary & Secondary Air Systems
- Piping & Ducting
The front, rear and side walls of vertical pass 1-3 of the Boiler system, along with the ignition roof, burnout roof and chutes from the boiler to the conveyor were all insulated with 140mm of mineral wool insulation. However, they were clad with different specifications of prefabricated sheet metal – manufactured in our fabrication facility. The walls were clad with 0.7mm profiled Aluzinc, the chutes 0.9mm flat Aluzinc and, in addition to 0.7mm profiled Aluzinc, the roofs had 4.5mm aluminium checker plate installed because they were required to be ‘walkable areas’.
Compared to vertical pass 1-3, a thicker layer of insulation was applied to different areas of horizontal pass 4: the roof (210mm), rear wall (200mm) and the hoppers underneath (240mm). This is due to operating temperatures of the different areas being higher than vertical pass 1-3 (130°C). Therefore, more insulation is required to maintain temperature/ reduce heat loss as well as lessen heat transfer to the external cladding, achieving safe touch temperatures for anyone who came into contact with the equipment.
Horizontal pass 4 (walls, roof and hoppers underneath) of the Boiler system were clad with 0.7mm profiled Aluzinc cladding. The cladding of horizontal pass 4 was secured utilising the DUK Sub-construction System (DUK). The DUK system provides a substantially stronger base to fix the cladding to and allows the insulation material to be pierced and held in place, something which is particularly beneficial when installing multi-layer insulation systems like was required on horizontal pass 4.
In comparison, due to its cylindrical shape, the boiler drum required a bolted spacer ring substructure to be installed, before being insulated with 130mm of mineral wool insulation and finished with Aluzinc cladding.
The continuous and atmospheric blow down tanks related with the Boiler system were insulated with 70mm and 40mm respectively of mineral wool and clad with 0.9mm flat Aluzinc cladding. The continuous blow down tank required thicker insulation due to its operating temperature being 184°C compared to the atmospheric tank which operates at 100°C.
Within the Primary and Secondary Air systems of the Common Steam Piping (CSP), our Insulation Operatives installed 100m thick acoustic insulation to the primary and secondary air fans. This insulation material is installed to reduce the amount of ‘noise’ produced by the fans when operational. It helps ensure health and safety compliance; keeping acoustics at a safe level for site personnel working in that area of the plant. The fans were finished with prefabricated 0.9mm flat Aluzinc cladding.
In addition to equipment, associated pipework for the Boiler/ CSP systems also required industrial insulation and sheet metal cladding installations. Over 3,500 lin/m of pipework was insulated with mineral wool pipe section and clad with Aluzinc cladding, both in various thicknesses depending on the operating temperature and size of the pipework. Teams also insulated 2,000+ lin/m of pipework but didn’t install cladding as this pipework was in situ under the cladding installed on the Boiler system so cladding was not required.
More than 450 Flexible Insulation Covers for the Boiler/ CSP systems were custom manufactured in-house and installed on valves, flanges, instruments and filters to name a few.
Flue Gas Treatment (FGT)
Powertherm expertly applied insulation to several pieces of equipment within the FGT system.
Mineral wool insulation, covering more than 3,000m², was applied to the filter chambers with a thickness of 100mm, along with 0.9mm profiled Aluzinc cladding to the outside surfaces and the DUK substructure system.
This phase of the project was completed at ground level, with the chambers lifted into place and connection pieces installed in situ; this provides a significant saving on scaffold access requirements. The correct application of the insulation system is crucial for temperature control, heat conservation and condensation control within the chambers. Excessive moisture can occur from too lower temperatures within the chambers; when the high temperature processing gas hits the chambers, any moisture in the air can condense, clogging up the filter bags and causing operational problems.
Powertherm’s Insulation teams also applied insulation and cladding to other assets within the FGT system, including the:
- Reactor;
- Raw & Clean Gas Ducts;
- Filter-ID-Fan-Stack;
- Preheating Ducts;
- Recirculation Channel;
- Boiler to Reactor & Rector Inlet;
which, with operating temperatures of 135°C, were all covered with 100mm mineral wool insulation to achieve the required thermal performance, with a total coverage of over 3,500m².
A rolled DUK substructure support system was utilised to support the cladding on the reactor; this means that the rail which the cladding is secured to was rolled (curved) – by our in-house Fabrication team – to meet the contours of the equipment. As with the chambers, the reactor scope was completed at ground level before being installed, connected and finished in situ.
500+ Flexible Insulation Covers associated with the FGT equipment were also measured, designed and manufactured in-house, before being installed onsite to valves, flanges, doorways, hoppers and the filter roofs.
Water Steam Cycle
The Water Steam Cycle (WSC) system was professionally insulated and clad by our Thermal Insulation Contractors Association (TICA) qualified Insulators. Equipment in this area of the power plant included the bypass condenser, feedwater tank, evacuation unit and associated pipework.
Covering 643m² (equipment) and over 5,500lin/m (pipework), the insulation and cladding within the WSC was meticulously fabricated and fitted to meet the specific requirements of each component, with thicknesses optimised for thermal efficiency and operational safety in line with operating temperatures. Key applications included:
Powertherm’s Flexible Insulation Products division also designed, manufactured and supplied over 1,500 Flexible Insulation Covers to fit relevant valves, flanges, filters, instruments and steam traps within the WSC system.
Solid Handling System
The industrial insulation scope of works within the Solid Handling (SH) system included providing solutions for the residue discharge/ transport, pneumatic ash transport ECO and the boiler ash discharge equipment.
The pneumatic ash transport, and residue discharge/ transport equipment, including the compensators, nozzles, inspection openings, gate valves, maintenance access and supports had 60mm insulation and 0.9mm flat Aluzinc cladding installed. The DUK Sub-construction System was installed on the pneumatic ash transport as the equipment is generally flat sided making the DUK the right substructure solution to support the insulation material and cladding in this instance. However, for the residue discharge/ transport, both spacer support rings and the DUK system were required due to the different shapes and sizes of the different sections of equipment.
Typically, Powertherm would recommend installing the DUK system on flat surfaces, a rolled version of the DUK on significantly sized curved surfaces, and support ring systems such as bolted or welded spacer systems on curved surfaces where the DUK cannot be rolled to meet the contours of the equipment because the circumference is too small.
Learn more about the substructure systems we install here >>.
The boiler ash discharge was installed with mineral wool insulation (60-160mm) and Aluzinc (0.9mm flat) cladding. Furthermore, within the boiler ash discharge, 50m² only required perforated cladding for personnel protection requirements, with no insulation installed. In some cases, insulation isn’t required as equipment needs to lose heat for process requirements, but cladding is still required to protect personnel from the high temperatures.
Total coverage of insulation/ cladding on these sections of Slough Multifuel was over 500m².
Balance of Plant (BoP)
The process water tank which fell within the Balance of Plant (BoP) scope was installed with 0.9mm flat Aluzinc cladding for personnel protection requirements. The cladding was secured using the DUK Sub-construction System.
The DUK Sub-construction System is the most robust substructure system available. The system is simple to install yet highly effective in use, with many benefits. It comprises of steel spacers which are fixed (welded) to the surface of the asset being insulated. The insulation material is pierced upon the spacers, reducing the need to cut it, whilst retaining its integrity. The coupling elements are fixed into the C-profile rail before being mounted onto the spacers. Cladding is then fixed to the railings with self-tapping screws.
The modular design of the system allows the couplings to be moved along the C-profile rail and positioned so that they ‘miss’ stiffeners and support structures. In addition, thermal expansion/ contraction is accounted for and managed through the allowance of movement between the coupling and spacer and the ability for fixed and loose points through horizontal/ vertical installations. The rail can also be ‘rolled’, providing a curvature to the railings for installations on cylindrical surfaces (5m dia minimum) like chimneys and round ducts for example. The WUS coupling has acoustic dampers integrated into it which provides a reduction in sound transfer to the outer cladding by >20dB (approx).
Also, within the BoP scope, over 1,200 lin/m of process pipework was insulated with 25mm thick mineral wool pipe section, with operating temperatures ranging from 60 to 120°C. After installing insulation, teams applied 0.5 or 0.7mm prefabricated Aluzinc cladding (depending on pipe specification).
More than 450 valves, flanges, filters and instruments associated with the BoP required Flexible Insulation Covers for thermal efficiency, personnel safety, and ease of operations and maintenance. All of which were designed and manufactured in Powertherm’s manufacturing facility, before being installed on-site by our insulation team.
Flexible Insulation Covers provide the typical benefits of insulating: heat conservation/ managing heat loss, reducing energy consumption and improving overall process efficiency for example. Whilst also providing safety benefits for personnel; preventing potential burns or injuries.
In addition, using Flexible Insulation Covers instead of traditional mineral wool and sheet metal cladding, as used elsewhere on this project, offers innovative advantages. These covers are typically secured with Velcro fastenings and draw strings, making them easy to remove and reinstall. This design facilitates quick and non-destructive access to components for operations or repair and maintenance needs, ensuring the required insulation is in place whilst being removable.
Trace Heating
Our Trace Heating team installed electrical trace heating systems around the plant to ensure systems/ equipment were either maintained at a specified temperature for process requirements or to provide protection from frost.
Temperature Maintenance
7,948 linear meters of mineral insulated (MI) heating cables were installed for temperature maintenance requirements to process equipment such as hoppers and associated pipework. As part of the waste burning process, ash naturally collects within the hopper units. If this ash isn’t managed correctly, it will solidify when moisture mixes with it, clogging up the hoppers and causing operational problems. The trace heating system stops this from happening by maintaining the surface temperature of the hoppers at the required level to prevent moisture build up and the ash above its dew point.
Firstly, technical Welders from within our Insulation Division welded insulation pins to the hopper surface which, along with helping to support the associated insulation material, served as fixing points for the trace heating system. Next, wire mesh was cut to size and secured using speedy washers.
Prior to being installed, the heating cables underwent a pre-install test to check their functionality. MI heating cables were then applied to the mesh using wire ties, followed by a pre-lag test of the MI cables, again to confirm the cables were working as expected.
Using brackets, junction boxes were then installed on the hoppers, with connections made to the junction boxes, and temperature sensors also fitted. The heating elements were foiled in preparation for the installation of the insulation system. Finally, a post-lag test of the MI cables was conducted to ensure the system’s integrity.
Frost Protection
958 linear meters of self-regulating heating cable was applied to process pipework for frost protection purposes. When the temperature drops to 5°C or less, sensors will pick-up the lower temperature reading, causing the trace heating system to energise. This in turn will provide heat through the self-regulating cables; ensuring the pipework does not freeze by raising its surface temperature.
The installation process of the frost protection system began with the pre-install testing of the heating cables to verify their functionality.
Following this, the self-regulating heating cables were installed directly onto the pipework. Junction boxes were mounted onto the pipes using pipe mounted brackets and steel banding. The cables were then terminated, end sealed, and connected to the terminals, with sensors fitted to the pipework as needed.
Learn more about our technical industrial insulation solutions and how we support leading companies here >>