Mansfield Pollard complete complex ventilation project for GRREC
In February 2016 Mansfield Pollard was approached by Interserve Construction Ltd to assist them with the design and implementation of a mulch dryer bypass system for the new, state-of-the-art Glasgow Recycling and Renewable Energy Centre (GRREC).
The £154m GRREC facility will handle 200,000 tons of council green bin residual waste every year; work in combination with city wide blue, brown and purple bin recycling; divert 90% of green bin residual waste away from landfill, saving millions of pounds; release recyclable resources from household waste; produce enough energy to power the equivalent of 22,000 households and heat the equivalent of some 8,000 homes; deliver a saving to Glasgow of 90,000 tons of CO² every year; as well as saving the city approximately £254m during the 25 year contract.
Interserve Construction Ltd had engaged with several specialist ventilation suppliers but to date, none of the companies that they had approached felt they had the technical ability to provide a system, which would meet all of their design requirements.
As Mansfield Pollard has its own in-house design capability and specialist controls divisions, the air management experts could marry the two together to overcome the challenges faced by Interserve Construction Ltd in implementing the system.
The design brief was to provide a bypass ventilation system from the mulch dryer. The dryer takes the waste from the city of Glasgow, after segregation and processing a sludge is created, this sludge is then passed through a dryer to create briquettes for gasification to drive the turbines and produce electricity. The hot gas exhaust from the dryer then enters the main extract system. At full capacity, this heat input into the system amounts to sum 900kw of thermal energy. The main extract system serves the whole facility and in winter the extract air temperature can fall to quite low temperatures. This air is eventually passed through a biomass filter to remove odours before being discharged to the atmosphere. The heat generated by the dryer ensures that the temperature within the bio-filter remains above 7 degrees Celsius to keep the bacteria alive which is used to reduce the odours.
The biomass filter and extract system operates at a fixed mass flow rate whilst also requiring a minimum temperature, yet the sludge dryer will vary its output both in flow rate and temperature dependent upon the sludge throughput. The challenge put to Mansfield Pollard was to provide a balanced bypass system with heat input to ensure that the air entering the main extract system, maintained a constant mass flow rate and air at the biofilter was kept above 7c.
Mansfield Pollard’s engineers designed an air bypass system connected to the output of the dryer. This consisted of four staged 225kw direct fired gas heaters with modulating dampers, filters and flow measuring devices. Temperature, pressure, and flow sensors were located at strategic locations on the system and as the dryer reduced its output, signals are sent to the 4 heater branches to modulate the dampers and proportionally fire the heaters to maintain the desired conditions. If the dryer is switched off, the bypass system provides the system with 900kw of thermal energy and 10.8 m3/s of air. A small bleed air system was incorporated into the discharge of the dryer to allow a very small amount of air to pass through the dryer and prevent the build-up of noxious or potentially dangerous gasses.
The installation of the system posed its own challenges. The system could only be installed after the dryer was in place with the ductwork, heaters and dampers installed some 12m up in the air. Meticulous planning was carried during the design phase to ensure the systems could be accessed for service and maintenance. The equipment was arranged so that gantries could be installed to allow access to as much equipment as possible from one location and facilitate the replacement of key components in service with minimal interruptions.
The whole site was managed by a Siemens distributed control system, which provided Mansfield Pollard’s system with set points and enables signals from the remote monitoring control room. As part of the installation, the team provided status feedback and safety interlocks communicated back to the DCS through a BacNet to Profibus translator. To ensure close integration with the main DCS Mansfield Pollard generated a vast amount of documentation including PID’s, system operating descriptions, signal exchange lists and schedules, all for sign off by Capula, the system integrator before work could commence.
The system was successfully handed over in March of this year and Mansfield Pollard continues to support Viridor during their site validation phase. As the temperature falls through winter Mansfield Pollard will be supporting Viridor in carrying out winter validation. Rob Knight, Senior Commissioning Manager at Viridor stated: “Mansfield Pollard has worked closely with the commissioning team at Viridor to provide key supply chain deliverables at the GRREC.”
Paul Dresser, Commercial Director at Mansfield Pollard said: “This was by no means an easy project to deliver but the close partnership with Interserve and Viridor ensured we could successfully meet all the requirements of our client. To date, this project remains one of the most technically complex ventilation and control projects we have delivered.”