Forehill WTW Pesticide Removal

Scottish Water
August 2013 to June 2014

Full Project Details

Crown House Technologies provided the mechanical, electrical, instrumentation, controls and automation (MEICA) services for the new Granular Activated Carbon (GAC) plant. This process removes pesticides from the water supply to the Peterhead area, and the new building houses seven granular activated carbon filters supplied by four process systems.

Our role

The design solution comprises GAC treatment with the carbon media (adsorber) contained in reinforced concrete tanks, housed within a steel portal frame superstructure. Waste water generated from the process is transferred to a waste stream splitter chamber, before discharge to buffer tanks for onward pumping to the existing sewer network.

CHt’s project team and Digital Engineering (DE) engineers drove the project design team to allow a fully integrated model. The client’s operational requirements were fully investigated to allow incorporation into the modular design. CHt fully commissioned the process utilising in house commissioning engineers.

The challenge

The challenge was to engineer a solution to achieve the reputational ‘Water in Service’ date given by Scottish Water to the local population.

Scottish Water had committed to this milestone set at 31st March 2014, but due to a delayed award of contract, the original tender programme date was some nine weeks later.

This project team’s decision to use prefabricated modules of the size, weight and complexity was to be a first within the Scottish Water portfolio of projects.

The pesticide removal plant needed to integrate with the existing plant for control of the final input stage of the process.

The client had no previous DfMA experience on this scale, and so it was crucial to gain their buy in from the outset. Client confidence with the DfMA process was achieved through the provision of detailed experience examples of past projects, and explanation of the DfMA approach that would be incorporated within the project.

The tolerances required for the 86 civil to mechanical service interface points dictated a stringent approach to precision within the model. All cast in-wall couplings were surveyed after installation with these measurements fed back into the model. Where possible, by manipulating the pipework layout in the digital model, tolerance between the connection pieces was incorporated, but due to spatial restrictions in the trench, considerable supply chain interfacing was required to ensure the required tolerances were met.

The client timescale restraints for pesticide removal to regulator limits necessitated an extremely aggressive programme. The size, cleanliness and complexity required for the North Service Trench would not have been achievable within the project’s programme duration without CHt’s DfMA approach. The Health & Safety risks associated with a conventional installation method within the service trenches would have proved extremely challenging and protracted.

The integration of this new process element into the existing system, without detrimental effect to the plant output, required careful planning and a collaborative working partnership with the plant operational staff.

Our approach

CHt provided fully integrated mechanical and electrical modular units into the project design. This DfMA approach was essential for the project to meet the client’s deadlines, with a reduction in M & E installation of approx 14 weeks.  

CHt led the design team in an upfront solution to allow a DfMA tailored methodology to be developed. The 3D model was controlled by CHt Digital Engineering specialists to allow thorough checking of interfaces and adherence to the protocols.  

The modules were designed for maximum transportable dimensions to provide minimal lifts to completion. The full 30m long North trench modular installation was positioned into the trench in one day.  

The 11 dry well pump skids were installed within a three day period. The design of the MCC kiosk was challenged by CHt and resulted in a modular installation complete with pre-installed containment instead of a conventional build on site.  

The electrical design was also challenged by CHt which resulted in, not only a DfMA solution being chosen, but a more robust and progressive commissioning solution for individual filter bed controls. This assisted in the staged handover of filter beds. The distribution board assemblies were also manufactured off site and installed over one week.  

The resultant programme saving for these elements was 14 weeks.

The engineering behind our delivery

The use of 3D Digital Engineering modelling was another first for Scottish Water on this type of project. This model has proven to be a very effective and crucial element in the Approval of Contractor’s Design meetings and HAZOP meeting with the assets operators. The ability to visualise operational elements before they were constructed impressed Scottish Water and improved the approval process.  

The project incorporated a dry well pumping station incorporating three process pumping sets, a trench pipe gallery, an Intelligent Control and Instrumentation system, a telemetry system with interface to existing system set-up, a new MCC and kiosk, building ventilation system, security and fire alarm systems, power and lighting.  

A robust three element checking procedure was implemented between engineers from CHt, Expanded and the CHt Manufacturing team from Oldbury. The digital engineers providing connection co-ordinates to site then site returning as-fitted survey results. These survey results were checked against the model and then forwarded to Oldbury for module checks. No modules were released for delivery until these checks were satisfied.  

Modular wiring was introduced to supply power and lighting within the service trench. Lighting and heaters were prewired on the modules. The control and power cabling for 28  Rotork valve actuators and 7 flow meters were installed on the modules.